STQDCES ON THE DIGENKTEO TREMATODES. 391

Studies on the Structure and Classification ofthe Digenetic Trematodes.

ByWilliam Nicoll, M.A., D.Sc,

of the University of St. Andrews.

With Plates 9, 10.

THE following work was commenced about the middle of1907 at the Gatty Marine Laboratory, St. Andrews, underthe Carnegie Trust Research Scheme. The greater part of itwas done privately in the Pathological Laboratory, UniversityCollege, Dundee, and it was concluded at the Marine Biolo-gical Laboratory, Millpoi't, under a Government (RoyalSociety) Grant.

My best thanks are due to very many friends for assistancein various directions, and in particular to Professor Mclntosli,of St. Andrews, for continual encouragement and suggestions,and to Professor Sutherland, of University College, Dundee,for granting me the privilege of working in his laboratoryand for helping to elucidate several pathological difficulties.

In this paper an attempt has been made to allocate each ofthe forms dealt with to its approximate systematic place—amatter of considerable difficulty in many cases. At thepresent time a classification of the digenetic Trematodes in thetrue sense of the term can hardly be said to exist. Toattempt to define a higher systematic unit than the genus isattended with much risk. A considerable number of sub-families have certainly been created, but few of these consistof more than two or three genera, and are really at most tobe considered as indications according to which classificationmay be expected to proceed. The formation, however, of

VOL. 5 3 , FART 3. NEW SERIES. 28

892 WILLIAM NICOLL.

these groups or sub-families and the examination of theirrelationships seems to be of the greatest importance inleading up to the natural family groups. On that account Ihave endeavoured—not in every case with success—to includeeach of the genera described here in some sub-family group.

Many systematic difficulties have been encountered in thecourse of this Avork, and I should like here to refer to thecase of Oampula oblonga Cobbold. It is almost a certaintythat the form I am describing as Brachycladiumoblongum (Brn.) is actually identical with Oobbold's species,but according to the strict laws of nomenclature the name notonly of Oobbold's genus but also of his species must beregarded as nomen nudum. I have followed in this matterthe authority of Looss and Odhner, but it seems to me thatthis particular species has been submitted to a test which,were it to be applied as rigorously, would prove fatal to manyof the species and genera of older writers. There appears tobe no escape from the trammels of nomenclature, and theonly hope of simplifying matters consists in the submittal ofeach new or x'e-described species or other systematic unit toas strict a scrutiny as has been done in the case of Campulaoblonga. This can never be done effectually so long as thework of criticism remains in the hands of isolated individuals.There is undoubtedly a need for some central scheme, as hasbeen already advocated more than once.

The general anatomy and histology of the Trematoda hasbeen the subject of fairly exhaustive reseach, yet a few pointsstill remain doubtful and disputable, e.g. the function of theso-called subcutaneous glands and the large cells of thesuckers. The myoblastic nature of these cells, as demonstratedby Bettendorf, can hardly be said to have been conclusivelyproved, or at any rate some modification and extension oEBettendorFs original views is necessary. The large cells ofthe suckers appear to have little in common with the sub-cutaneous cells. In appearance and staining properties theyresemble true nerve-ganglion cells. The subcutaneous cellsbear a much closer resemblance to the small cells of the suckers.

STUDIES ON THE DIGBNKTIC TBEMATODES. 393

Few new results of a general nature are offered in thefollowing notes. On the other hand, there are many apparentredundancies. These are only to be excused on the groundthat the tendency to increased differentiation of specific forms,together with the fact that in numerous cases a formpreviously considered as a single species has on careful studyof its anatomy and histology been subdivided into two or moredistinct species, renders it necessary to give as full a descrip-tion of the form dealt with as possible. In this connectionreference to a much discussed paper of Stafford's1 can hardlybe omitted. Looss3 has already expressed what must be theopinion of every systematist on this paper. Such a methodas Stafford has employed is unpardonable even in a " pre-liininai-y contribution," and can hardly fail to cause endlesstrouble and confusion. By the laws of nomenclature Stafford'sgeneric names, except where preoccupied, must be regardedas valid, for he is presumed to have in his possession type-specimens of the several genera which he has named, or atany rate type-specimens must be supposed to exist somewhere.3

For this reason Stafford's generic name F e l l o d i s t o m u mlias been adopted here, although strictly speaking the nameF e l l o d i s t o m u m is really synonymous with L e i o d e r m aStaff, (and therefore with S t e r i n g o p h o r u s Odhn.), for thereis absolutely no difference of generic importance in Stafford'sdefinitions of the two genera. His definition of F e l l o -d i s t o m u m is actually a recapitulation of his definition ofthe preceding genus L e i o d e r m a , and the only difference issummed up in the sentence, "Many resemblances to Le io -d e r m a , but with sucker and genital glands crowded back-wards." No mention is made of the position of the genitalaperture, the absence of oesophagus, or the condition of the

1 " Trematodes from Canadian Fishes," in' Zool. Anzeig.,' xxvii (1904).pp. 481-495.

: " Revision of Hexniurida3," in ' Zool. Anzeig..' xxxi (1907), pp.587-620.

'•' Unfortunately this does not work out satisfactorily in every case.To my request (July, 1908) for type-specimens of several of his generaDv. Stafford lias vouchsafed no reply.

394 WILLIAM NICOLL.

uterus and ova, which, as Odhner has in part indicated, andas I have tried to show, are really the generic features dis-tinguishing Fellodistomum from Steringophovus.

Amongst the various histological features to which attentionhas been paid are the size of the muscle-fibres and of theelements of cellular structures. These, however, dependingas they do so much on the state of contraction and themethod of preservation, can hardly be considered of muchpractical utility. Other features of more importance whichhave been dealt with are the nature of the yolk-glandsecretion (see under Stephanophiala laureata), the intes-tinal epithelium, and the cellular elements of the suckers inFellodistomum fell is.

Reference may be made here to an interesting bionomicproblem, which unfortunately does not admit of easysolution, namely, the length of time required for the cercariato attain maturity on entering its final host. It is easilyascertainable that it does not commence to produce ova,which may be regarded as the criterion of maturity, im-mediately on entering its host. A longer or shorter period oftime usually elapses, during which it increases considerablyin size. The question has occurred to me in connection withvarious species, and here particularly in the case of Lebo u riaidonea. It has been a matter of frequent observation thata certain definite size limit exists between immature andmature specimens, or, in other words, that egg-productionbegins at a more or less constant period. In the case ofLebouria idonea the smallest mature specimen measured16 mm. and the largest immature specimen was of the samelength. Again, in Podocotyle atomon the limit of matu-rity appears to lie somewhere between "9 mm. and l'O mm.Many other examples might be given, but these will serve asillustrations. The smallest individuals found in the abovetwo cases measured respectively 1*0 and -65 mm. It is fairlycertain, however, that the cercarise in each case are some-what smaller thau the above minimum limits, but takingthem at those lengths it is evident that the cercarise must

STUDIES ON THE DIGENKTIO TREHATODBS. 395

increase in length by at least half before attaining sexualmaturity. This, of course, does not hold good in everyinstance, for in some species the proportionate increase issmaller, while in others it is larger.1

That Distomids, like other animals, have a fairly constanttnatui-ity-size might have been deduced from analogy. Theproduction of ova as the test of maturity is open to obviousobjections. It might be held that the animal is mature whenthe genitalia are developed, and that egg-production need notproceed immediately although the animal continues to grow.Against this must be put the fact of the constant line ofdemarcation in size between specimens with ova and thosewithout, and further, that a Distomid of adult size withoutova is a rarity. Admitting that such a line of deniai-cation doesexist, and that it is constant within close limits of variation,we should here have what might possibly be a valuable aidto diagnosis between nearly related species. As an examplemight be taken the case of the species of the genus Levin-senie l la . I have previously described a mixture of two ormore of these as S p e l o t r e m a fe r i a tum n. sp. (see later).They wei*e found in five different species of birds. In three ofthese the Distomids were fully mature, but in the other two,namely, Hasmatopus and Vane l lus , they were quite im-mature, although of the same size, or even larger. I haveexamined several specimens of both these birds at differentseasons of the year and found the pai'asites fairly frequently,but never in the mature state. The probability is that thelatter specimens represent a species distinct from that occur-ring in i E g i a l i t i s and Pe l idna .

In the determination of the identity of similar parasitesoccurring in different hosts certain additional factors mayenter, and it is to these that at several times by various authorsvariations in a particular Distomid inhabiting more than onefinal host have been ascribed. Differences of less or greaterdegree in external and internal characters, amounting in

1 Looss deals with the same matter in " Distonien miserer Fische undFrosclie," ' Bibliotheca Zool.,' vi (1894), p. 240.

396 WILLIAM N1C0LL.

many cases, as easily proved by later research, to specificdistinction, have been attributed to the different environ-mental conditions in different hosts. That the variation insuch cases is to be explained by the environment is not at allcertain, and it is very probable that on careful examinationthe same amount of variation would be found in specimenscollected from the same host. Certain features are capableof varying within comparatively wide limits and can bemeasured with sufficient precision, e . g . the size of the ovaand the extent of the yolk-glands. A case in point is that ofP o d o c o t y l e a tornon (Rud.), which occurs in a largenumber of different fish. In this species the ova were foundto vary considerably in size, and a list was given1 of the sizeof the ova in specimens from four different hosts, whichapparently showed that there were different limits of variationin each case. These measurements included a fair number ofexamples, but not nearly sufficient to determine the utmostlimits in each host. One thing the list does show, however,is that in no particular species of fish are the ova distinct insize; such a variation, otherwise, would be sufficient toindicate specific distinction. I have since found in a singlespecimen of G-astrsea s p i n a c h i a a species of P o d o c o t y l ewith ova greatly exceeding those from the fish alreadyreferred to and yet not differing in other respects fromP o d o c o t y l e a t o m o n . I t is difficult, on this account, tosay what effect, if any, environment may have on Distomidpai-asites, or whether the observed variations are purely theresult of fortuitous circumstances. The question appearsworth solving, $md I hope to be able to publish later someobservations on the same species found in numerous fishesfrom the west coast of Scotland.

The following is a list of the species mentioned in thispaper, with their hosts and habitat:

1 " Entozoa of British Marine Pishes," in ' Annals and Mag. Na<.Hist.' (7) xix, p. 76.

STUDIES ON THJK DIUENE'HO TKMMATODES. 3H7

Stephanophiala (n.g.) laureata (Zed.)Stephanopbiala transinarina n. sp.

Brachycladium oblongtini (Brn.) .Brackycladium sp.Leboiu-ia (n. g.) idonea 11. sp..Lebcraria obducta n. sp.(Lebouria) tumidula (Rud.) ¥Podocotyle atomon (Rud.)

= Dist. vitellosum Johnstone .

Cainocreadium(n. g.) labracis (Divj.)Peiucreadmiu (n. g.) gemi (Rud.) .Feracreadium comimme (Olsson) .(Lepocreaditun) serospinosum sp.

inq. . . . . .= Dist. globiporum Linton e.p.

Zoogonus rubellus (Olsson) .Fellodistomuni fellis (Olsson)Fellodistomuin agnotam n. sp.

Steringophorus clutliensis n. sp. .

Plagiorchis notabilis n. sp. .

Spelotrema claviforme (Brandes) .

Spelotrema simile Jagersk. .Spelotrema excellens Nicoll .

Levinseniella bracliysoma (Orepl.).= Spelotrema feriatum milii, e.p.

Levinseniella sp. .

= Spelotrema feriatum milii, e.p.

Toeotrema jejumim Nicoll

Salmo farioSalvelinus fontinalisSalmo mykissPhoctena commimisPhocsena commimisAnnarrkichas lupus.Bairdiella chrysuraLabrus bergyltaPleuronectes flesusPleuronectes platessa.Gadus virens.Gadus pollachius.Labrax lupus .Labrus bergyltaLabrus bevgylta

Intestine.

Intestine.

Liver.Liver.Intestine.Intestine.Intestine.Intestine.

Intestine.Intestine.Intestine.

Leiostomus xanthurus Intestine.

Anarrhichas lupus .Anarrliichas lupus .Anarrliicbas hipus .

Pleuvonectes micro-cephalus ' .

Antlius obsctirusMotacilla flavaPelidna alpinajEgialitis hiaticula •Antlius obscurusNumenius arquata .jMotacilla flavaLarus ridibundus .Larxis ridibundus .Larus argentatus .

Pelidna alpinaTotauus calidris^jgialitis biatic\ila .Hsematopus

ostralegus.Vanellus vanellus .Numenius arq\iata .Larus ridibundxis .Totaniis calidris

Intestine.Gall-bladderGall-bladder

andduodenum.

Intestine.

• Intestine.

Intestine,> cseca and

rectum.

Intestineand cseca.

•) Intestine,> cseca andJ rectum.

Intestine,caeca andrectum.

Intestine.

398 WILLIAM NICOLL.

Cryptocotyle concava (Crepl.) . Pbalacrocorax ~\ Intestine,graculus . [ cseca and

J rectum.Gytnnopkallus dapsilis Nicoll . Oideniia nigra . "J Bursa

Oideniia fusca • 3 Fabricii.Maritrenia liuniile Nicoll . . Totantis calidris . Intestine.Maritrenia lepiduin Nicoll . . Larus argentatus . Intestine.Maritrenia gratiosum Nicoll . . Larus ridibundus .]

Pelidna alpina . jiEgialitis hiaticula. )• Intestine.Hsematopus

ostralegus

Sub-family STKPHANOPHIALIN ;, n. sub-fam.

G-enus Stephanophiala , n. g.Stephanophia la laureata (Zeder). PI. 9, figs. 1-5.

Distoma laureatum Zeder, 'Nacht. z. Naturg. d. Einge-weidew./ p. 192; Eudolphi, cBntoz. Hist./ ii, p. 413;' Synops./ pp. 113 and 413; Dujaidin, ' Hist. d. Helm-inth/ p. 435; Olsson, 'Kgl. Sv. Vet. Akad. Handl./1876, Nr. 1, p. 21, PI. iv, figs. 52-54; ? Linton, ' Eept.U.S. Commiss. Fisheries for 1889-1891' (published 1893),p. 553, fig. 26-30.

Distoma farionis Mull. Blanchard, 'Mem. Soc. Zool.France/ iv, 1891, pp. 481-3, fig. 38.

Crepidostomum laureatum (Zed.) Braun, 'Annal.Hofmus. Wien./ xv, pp. 231, 232; Looss, 'Zool. Jahrbiich.Abtheil. Syst./ xvi, 1902, p. 452.

This fairly frequent parasite of the common trout (Salmofario) has been known for many years, and it has beenfound by vai-ious obsei-vers, who have each contributedtowards a knowledge of the species, but no connected accounthas appeared since Olsson's description in 1876. Althoughnot entirely free from error, this description is fairly accurate,but it is not sufficiently detailed for modern requirements.

STUDIES ON THK DIGJSNE'J'IC TREMATODES. 399

Blanchard completed the topography of the female genitalia,and Looss was the first to indicate the structure of thecircum-oral papillae. Several other important features remainundetermined. The systematic position of the species will bediscussed after a general account of its anatomy has beengiven.

The distribution of this Trematode may not be confined toEurope, for Linton has described what appears to be thesame or a closely related species from an American trout(Salmo m y k i s s ) . No difference of specific importance is tobe found in Linton's description, but it is probable that thetwo forms are not quite identical (see p. 35).

My specimens were obtained in June, 1907, from two smalltrout captured in a tributary of the River Spey (North ofScotland). Each fish contained four or five examples of theparasite. In another two small trout, from a stream runninginto the River Tay (April, 1907) several immature specimens(fig. 5) were found. The intestine of one of these fish wasabsolutely crammed full of E c h i n o r l i y n c h u s a n g u s t a t u sRud. while only one Distome was present. This might afforda striking instance of what Hausmann1 .terms the mutualcrowding-out of parasites. Still another trout, of large sizebut in poor condition, was obtained later from the River Tay,but it contained no Trematodes. Four small trout wereexamined in May, 1908. They were also from the basin ofthe River Tay, but they did not contain D i s t o m u ml a u r e a t u m . A few specimens, however, of B u n o d e r an o d u l o s a (Zed.) were found in them. Olsson found theparasite from April to August, and Linton in July andAugust. I have had no opportunity of ascertaining whetherit was present during the other months of the year. Theoccurrence in April of immature specimens only is suggestive,but my material is obviously inadequate to admit of anyconclusion with regard to the life-history.

1 " Tiber Trematoden der Siisswasserfisclie," ' Revue Suisse Zool.,' v.This, however, can only be regarded as an occasional occurrence exceptin particular instances.

400 WILLIAM NICOLL.

The number of specimens occurring in one host is not verygreat, although Lintonputs it at as many as one to two dozen.Olsson says he found many specimens, but it is not clearwhether he means in each or altogether. Its frequency,however, is well established, and it is probably moreoften present than not, at any rate during the months ofApril to August.

The habitat is chiefly the middle reaches of the iutestine,but I have found it, especially in the immature state, as fardown as the rectum. The occurrence of young specimens ata lower level in the gut than the adults is characteristic ofmore than one species, and it is probable that the cyststraverse the whole length of the intestine before the cercariasare set free. Olsson records it. from the rectum and stomachof the trout, also from the pyloric appendages of Thymallusvulgaris . Linton found it in the rectum of Salmomy kiss.

It is easily discoverable in the intestinal contents, beingmoderately large and of a pale but distinctly reddish colour.Olsson says the colour is white, and the difference may be dueto the fact that my specimens were nod seen till twenty-fourhours ufter the death of the host, at which time the parasiteswere still alive, but very sluggish. There is no very obviousreason, however, for believing that that would account for achange in colour. For the above reason little movement wasobserved in the parasite, but it was apparent that the neck orpre-acetabnlar part was much more mobile than the rest ofthe body. The shape is elongated oblong, tapering towardseither extremity, but more or less rounded according to thestate of contraction; flattened dorso-veutrally. The con-tinuity of the anterior margin is interrupted by the projectionof two or more of the circuni-oral papillas. The surface ofthe body was thrown into irregular rugae, but that iscommonly seen in Trematodes some time after the death oftheir host. The length of my mature specimens is fairlyuniform—3-4 mm. ; the immature specimens are in manycases less than 1 mm. Most observers are agreed in fixing

STUDIES ON THE DiGKHETIO TKJSMATODKS. 401

the limits in size at 2-4 mm., but Olsson found examplesmeasuring as much as 6 mm. The gi-eatest breadth occurs at,or just behind, the ventral sucker, and is approximately onequarter of the length. This proportion is fairly constant.

The suckers are well developed and muscular. Theoral sucker is sub-terminal and round, bub not quiteglobular. In a specimen of 3"5 mm. length (to which allthe following measurements may be referred) its transversediameter measures "31 mm., while its antero-posterior diameteris usually slightly greater. Its aperture is nob exactlyciixmlar, being encroached on laterally, but to no great extent,by the part bearing the two ventral papillse. Tlie wall ofthe sucker is not of the same thickness throughout, theanterior dorsal part being much thicker than the remainder.Here the thickness is '093 mm.; the rest of the wall variedfrom "05 mm. to '065 mm. It presents a further peculiarityin that the thick anterior part is separated from the rest bya distinct constriction where the thickness is not more than•035--04 mm. The appearance suggests that the thick anteriorpart is a secondary growth from the main part of the sucker.The histological structure of the sucker represents what mustbe regarded as the typical Distomid structure. Externallyit is separated from the body parenchyma by a well-definedfibrous membrane. Its cavity is lined by a cuticular layercontinuous with the body cuticle, but somewhat thinner.Beneath this is a thin fibrous membrane continuous with theexternal membrane. Between the external and internalmembranes run the radial muscle-fibres arranged in groups,each containing from six to twelve fibres. The latter mayattain a diameter of "0045 mm., but this naturally varies withthe state of contraction and is usually not more than "002mm. The groups are separated from each other by spaces inwhich lie one or more cells. The anterior swelling is alsotraversed by radial fibres more closely arranged, and radiating,fan-like, from the inner membrane to the outer. Their courseis not straight but curved (fig. 2). Close beneath eachmembrane there is a series of circular muscle-fibres, arranged

402 WILLIAM NICOLL.

singly, one fibre being situated between the ends of adjacentradial fibres. Their diameter is about 'OOOG-'OOIS mm., butthe fibres of the external layer are somewhat stouter thanthose of the internal layer. Two distinct varieties of cellsare met with in the sucker. The most numerous are small,rounded cells, which stain uniformly purple with hEemaluin-eosin, and their nuclei are differentiated only by their darkercolour. They are situated for the most part closer to theexternal membrane than to the internal membrane. Severalfilaments are given off by each cell. The other variety of cellis distinguished by being much larger and by different stainingreaction. The cell body is not well defined, but the nucleusis large, conspicuous and round or oval in shape. It stainslight pink, with a clear zone externally and a more granularzone internally. "Within it is a small round nucleolus,staining bright red. These are the ruyoblasts, and they liein the spaces between the groups of muscle-fibres and usuallymidway between the outer and inner membranes of thesucker.

The circum-oral papillas are, as Looss has already pointedout, outgrowths of the muscle substance of the sucker. Theyare six in number, two being distinctly ventral and fourdorsal, and their bases are all situated on the same transverseplane. The ventral papillte are closely opposed to themargin of the aperture of the sucker, and their bases, asabove mentioned, occasionally give rise to two prominencesprojecting into the aperture; the other papillas are situatedequidistant from each other and from the ventral papillse.The shape is depressed, tongue-like; the size varies accordingto the state of contraction. In a transverse section of theirbase the measurements are >035--04 by -015--02 mm., whilethe length is about "03—"04 mm. The muscle-fibres of thepapillce are apparently finer than those of the sucker. Theycomprise both longitudinal and annular fibres. No myoblastswere observed in the substance of the papillse, but at thebase of each, situated in the sucker, there is usually at leastone myoblast apparently in connection with the papilla. A

ST0D1BS ON THE DIGENETIG TREMATODES. 403

feature of difference between the dorsal and ventral papillfBis due to the fact that the dorsal wall of the sucker is notclosely apposed to the dorsal body cuticle, but is separatedfrom it by parenchymatous tissue. The dorsal papilla)* infinding their way to the exterior have to pass through thislayer, and thus around the base of each dorsal papilla asmall swelling is formed by the parenchyma, and thisswelling is absent in the case of the ventral papillae, for attheir origin the wall of the sucker is contiguous with thecuticle and there is no intervening tissue. Still anotherpoint is to be remarked. The ventral papillae arise from thealready noted anterior swelling oE the sucker, but the dorsalpapillae arise from the main part of the sucker, immediatelybehind the swellings. This is indicated in fig. 2. Thiscircumstance seems to necessitate a modification of the viewsof Braun and Looss on the origin of the papillae. It canstill be maintained that the anterior swelling, together with thepapillae, represent the almost undivided suctorial swelling inRhytidodes gelatinosus (R.), but it is evident that inStephanophiala laureata the process of transformationhas gone much further than was supposed. Thus the divisionof the simple swelling has given rise, not only to distinctcontractile papillae, but four of these have been entirelyseparated from the original swelling and have been displacedbackwards.

The ventral sucker is situated near the junction of theanterior and middle thirds of the body. It is transverselyoval and nearly twice as large as the oral sucker. Its trans-verse diameter is "50 mm. and the longitudinal diameter *43mm., i .e. the diameter is about one seventh of the length oithe body. Its depth is "16 mm. and occupies nearly thewhole thickness of the body. The wall has an averagethickness of "057 mm. The histological structure is essenti-ally the same as that of the oral sucker, the muscle-fibresbeing, if anything, slightly stouter and the myoblasts pro-portionately less numerous. The sucker as a whole does notproject much above the surface of the body.

404 WILFJAM NICOLL.

A word must be said here with regard to the dimensionsof the suckers as stated by Olsson. Considerable discrepancyexists, which necessitates an attempt at explanation. Thesizes given by Olsson are •40--52 mm. for the oral sucker and•63—"75 mm. for the ventral sucker. These are evidentlymuch in excess of my measurements and cannot apply to aspecimen of 3-4 mm. in length. Olsson says they weremeasured from a " spec, adult," and by this lie must under-stand a specimen of 5-6 mm. in length. On this suppositionthe oral sucker would be about one eleventh of the bodylength and the ventral sucker about one eighth. Moreover,on careful measurement of Olsson's figure I find that thesuckei-s are respectively one eleventh and two fifteenths ofthe body length. According to Linton also the oral suckeris one eleventh and the ventral sucker one eighth. In view ofthis agreement it may be taken as a distinctive feature of thespecies that the oral sucker is one twelfth to one eleventh andthe ventral sucker one eighth to one seventh of the bodylength.

The cuticle has a fairly uniform thickness of '0025—"003 mm.The musculature of the body conforms to the usual type,

with the three subcutaneous layers, circular, longitudinal,and diagonal, and the less organised parenchymatous fibres.

Close underneath the layer of diagonal muscle-fibres lies alayer of what were formerly regarded as cutaneous glands,but which are, according to Bettendorf,1 the myoblasts of thesubcutaneous muscle-fibres. So far as can be gathered,Betfcendorf s views have not been completely confirmed, butthey are probably correct. At any rate the glandular natureof these cells has never been proved, and from Bettendorf'swork they appear to be in intimate connection with the sub-cutaneous muscle-fibres. These cells, as I have observedthem in this species, stain deep blue with hsemalum-eosin andthe nuclei are only differentiated by being denser. The cellsare rounded in outline with several filaments, and in manycases they appear fused together in groups of two or three,

1 ' Zool. Jahrbucli. Abth. Anat.,' x, 1897, p. 307.

STUDIES 0NT THE DIGENETIC TREMATODES. 405

so that the outlines of the individual cells are lost. Thesecells certainly do not resemble the large cells (myoblasts) ofthe stickers, the cell-substance being much denser. Theybear more resemblance to the smaller cells of the suckers,bub most of all to the circum-oesophageal and vaginal " gland-cells." The glandular nature of these latter cells is again amatter of: hypothesis, and their undoubted resemblance to the" subcutaneous glands" strengthens Bettendorf's views as totheir myoblastic nature. The same may be said with regardto the cells sui'rouuding the terminal portion of the dnctnsejaculatorius in the cirrus pouch. All these cells are easilydifferentiated from cells of which the glandular functionis well established, i.e. prostate gland and shell gland, evenby ordinary staining methods.

True cutaneous glands, however, do exist in this species,but they are i*estricted in extent. They occur in theanterior part of the body only, situated fairly deeply andscattei'ed throughout the region from the pharynx to theintestinal bifurcation. Similar cells (cephalic glands) appearto exist in many other species, but their occurrence has notbeen universally confirmed. They are not very numerous,but their number could not be estimated. Their ducts canbe easily demonstrated, as also the fact that a considerablenumber of them open around the oral sucker. They aresomewhat pear-shaped or tear-shaped, with their narrow enddirected forwards. They measure about "036 by "019 mm.,and their contents consist of a homogeneous, finely granularmaterial, staining light blue with haenialum-eosin, in themidst of which is a large round nucleus, "007 mm. in diameter,with distinct nucleolus. The function of these glands is stilla matter of opinion. According to Leuckhart andLooss theirseci-etion exercises an irritative action on the tissues of thehost, causing an increased flow of juice, and even, accordingto some authors, a flow of blood in certain cases. This seemsa reasonable enough supposition and is supported by theposition of the glands. It may also account for the fact thatsome animals, although harbouring an immense number of

406 WILLIAM N1COLL.

Trematode parasites, do not appear to suffer from theirpresence, but may indeed possibly benefit by the increasedstimulation of the gastric and intestinal glands. An alternativetheory with some claim to recognition is that the secretion ofthese glands renders the contents of the host's intestine lesstenacious and thereby facilitates the activity and locomotionof the parasite.

The alimentary system does not offer any strikingpeculiarity. There is a small pre-pharynx, with thin wallsand lined by cuticle continuous with that lining the oralsucker and pharynx. Into this the anterior end of thepharynx projects, so that, on external view, the pharynxappears to be continuous with the oral sucker.' In manyspecies the phaiynx is described as continuous with the oralsucker, but in most of those it will probably be found thata small pre-pharynx intervenes. One notable exception isR h y t i d o d e s g e l a t i n o s u s (Rud.), in which no pre-pharynxis present. The pre-pharyngeal vestibule gives the pharynxgreater freedom of movement, permitting, as it does, a certainamount of longitudinal movement, independent of the bodyextension and contraction, while at the same time it allowsthe anterior end of the pharynx to expand, somewhat afterthe manner of a sucker. The external membrane of the oralsucker is continued along the pre-pharynx on to the pharynx,which it invests. The pharynx is of moderate size, andnearly globular, but flattened dorso-ventrally. Its diameteris "15—"19 mm. and thickness '09—"10 mm. The lumen is anarrow, transverse slit, and the walls are about "(M-'OS mm.thick. The structure is identical with that of the suckers.The radial muscle-fibres have an average thickness of•0015 mm. and the circular fibres '001 mm. Towards theanterior end the muscle-fibres are very closely packed.Passing forwards the radial fibres are more and more obliquelyset, until they come to run almost parallel to the internalwall. Lacunar spaces are much reduced and cells are rare.Most movement apparently takes place at this part.

The oesophagus is about the same length as the pharynx

STUDIES ON THE DlttENETIO TliBMATODES. 407

(•15-2 mm.) and the intestinal bifurcation occurs a shortdistance in front of the ventral sucker. The diverticula areuniform and fairly wide, extending almost to the posteriorend of the body. The oesophagus is lined by a somewhatthick membrane (metamorphosed epithelium), the surface ofwhich is thrown into slight folds. This membrane is con-tinuous with the cuticular lining of the pharynx, but is thickerand stains differently. With hasmalum-eosin it takes on areddish-purple colour, whereas the cuticle is more distinctlyblue. The musculature consists of the usual internal annularand external longitudinal layer, the fibres being more ov lesswidely separated according to the degree of contraction.Surrounding the outer layer is a ring of very loose connectivetissue, on the outer edge of which are numerous small, blue-staining cells—the myoblasts of the cesophageal muscles.The diverticula separate at a wide angle and bend towardsthe outer side of the ventral sucker. The rest of their coarseis practically stoaight, with a slight turn in near the end.At first they lie midway between the dorsal and ventralsurfaces of the body, but on passing the ventral sucker theyassume an unvarying dorsal position and are surrounded onall sides except dorsally by the yolk-glands. The averagewidth of each diverticulum is about "08 mm. Their transversesection appears sometimes oval, sometimes triangular, andsometimes almost circular. The lining consists of a singlelayer of epithelial cells, with well-inai'ked nuclei and nucleoli.The nuclei measure '005—"008 mm. The cells are of irregularshape, with long fibrillar or hair-like processes stretching intothe lumen and filling it up to some extent. Amidst the cellsthere are numerous small vacuoles. The appearance presented,in fact, is that of a row of nuclei lying in the midst of a fibrousfeltvvork; the cell outlines are difficult to distinguish. Thisepithelial layer is absent in a small part of the diverticulajust behind the bifurcation, and is replaced by a continuationof the cesophageal membrane. This recalls the condition inPatagium brachydelphium Heymann, in Avhich theinitial part of the diverticula is constricted and devoid of

VOL. 5 3 , PAET 3 . NEW SERIES. 29

408 WILLIAM NICOLL.

epithelium. I t is thus histologically part of the oesophagus.This condition is of some structural importance. In otherspecies which I have been able to examine, and particularlyin the ALLOCREADiiNa;, the layer of epithelial cells is continuedright up to the junction with the oesophagus. The musculatureof the diverticula is the same as that of the oesophagus, but.the fibres are more irregularly spaced.

The excretory vesicle consists of a single undividedterminal sac, lying just under the dorsal surface of the bodyand extending as far forwards as the anterior border of theanterior testis, where it divides into two much narrowertubules running forwards to the level of the oral sucker.Over the testes the vesicle is compressed transversely, butelsewhere it is nearly isodianietric. The excretory pore isnot quite terminal but is displaced very slightly dorsally.In section the wall presents an irregular outline. The liningof the vesicle consists of a distinct but thin membrane, whichstains like cuticle, and under this there is a regular layer ofoval nuclei with their long axes parallel to the wall of theVesicle. No cell outline could be discriminated. The nucleipossess a distinctive character in the apparent absence ofnucleoli. They contain numerous chroniatoph.il threads andgranules staining rather dark blue, while the rest of thenucleus has a lighter tint. These nuclei can be tracedthroughout the greater part of the excretory system andappear to be peculiar to it. This lining membrane evidentlydoes not conform to the usual type, in which the epithelialcells are prominent in the wall of the vesicle and are sharplymarked off from the surrounding tissues. Here the cells arenot prominent, and they are in close relation to the adjoiningparenchyma.

G e n i t a l s y s t e m : The testes are two rounded or ovoidbodies, situated directly behind each other in the middle lineof the body. The posterior testis is about one quarterof the body length from the posterior end, while the anteriortestis is separated from the ventral sucker by a shorter space.They may be closely apposed to each other, or more usually

STUDIES ON .THE DIGENET10 TREMATODES. 409

separated by a narrow space occupied by yolk-glands,Their outline is slightly irregular, but not lobed. Theanterior testis is often hollowed out in front and transverselyelongated; it varies in size and shape much more than theposterior testis does. The antero-posterior axis measures"21—'28 mm., the transverse axis '26—'44 mm. The corre-sponding measurements of the posterior testis are "28—"43 mm.and ^-"SO mm. The average is about *27- by -34 mm. forthe anterior, and '34 by "33 mm. for the posterior. Thusthe diameter is rather less than one tenth of the body length.This result is in close agreement with the figures of Olssonand Linton.. Olsson, however, states that the testis exceededthe ventral sucker in size. That was certainly never thecase in any of my specimens, nor does it appear to be so fromLinton's figure.

There is no sinus genitalis, or at most it is representedmerely by a shallow depression, in which the male and femaleducts open separately but contiguously, the former in frontand to the left of the latter. In total preparations, however,only one aperture is sometimes seen. Its position is invariablymedian and exactly ventral to the posterior end of thepharynx. In Olsson's representation of the species (PI. IV,fig. 52) the apertures are shown widely separate, .but this isevidently the result of an erroneous observation, which I shallendeavour to make clear. The apertures are figured behindthe intestinal bifurcation, between it and the ventral sucker,and they appear to be separated by a distance of nearly "2 mm.Further, from the supposed male aperture a long penis isrepresented stretching straight forwards to about the middleof the pharynx, while the cirrus-pouch shows a somewhatelongated oval outline quite different from the pear shape ofmy specimens. To me it appears that the structures markedp and b in fig. 52 are really portions of the cirrus-pouch, bbeing the thicker posterior part and p the narrow anteriorpart or neck running forward to the genital aperture nearthe posterior end of the pharynx. The erroneous position ofthe female genital aperture is probably due to the fact that

410 WILLIAM NICOLL.

Olsson mistook the point beyond which the ova could not beseen for the termination of the vagina—a not at all unlikelymistake. On such a supposition my specimens agree verywell with those of Olsson, otherwise the difference is of morethan specific value.1 On this matter Linton says nothingdefinite, but his figures show the genital aperture wellforward in the neck, always single and sometimes withexserted cirrus. Careful measurements of his drawings,which we may assume to be drawn in proportion, show thatthe genital aperture is nearer to the posterior end of thepharynx than to the anterior border of the ventral sucker.In fig. 30, where the pharynx is not represented, the genitalaperture is about '19 mm. behind the posterior border of theoral sucker. The average length of the phai-ynx being *16 mm.it is evident that the genital aperture is not far behind itsposterior border.

The fact that Linton represents the genital aperturesiugle tends to cast some doubt on my observation of theabsence of a sinus genitalis. The exserted cirrus in Liuton'sspecimens might have obscured the double aperture, but itis possible that the condition as I observed it was purelyaccidental. Against this is the fact that it occurred in severalspecimens.

The cirrus-pouch is, as already mentioned, of the charac-teristic Distomid shape, with a wide posterior part containingthe vesicula seminalis, gradually narrowing into a slenderanterior part containing the terminal part of the ductusejaculatorius. The latter usually passes straight back fromthe genital aperture, and the thicker part is bent on it eitherto the left or to the right. I t extends back to the level ofthe centre of the ventral sucker. I t occasionally does not

1 By the kindness of Dr. Jagerskiold I have been enabled to examinetwo of Olsson's original specimens from Thymallus vulgaris andto confirm the correctness of the above suppositions. The genitalaperture (or closely apposed apertures) is situated midway between thetwo suckers and therefore not far behind the end of the pharynx. Itsposition is probably most correctly described as midway between thesuckers.

STDDIES ON THE DIGENETIC TREMATODES. 411

reach this level, but seldom, if ever, exceeds it. Its length is'45—"55 mm.; the maximum diameter is *12 mm., and theaverage diameter of the neck is -05 mm.

The pouch is a true muscular cirrus-pouch, and its wallconsists of the frequently described internal annular layerand external longitudinal layer. It thus differs essentiallyfrom that of Bunodera nodulosa (Zed.), in which the wallis purely membranous.

The structures contained within the cirrus-pouch conformto the common type, e .g . that of the ALLOCREADIIN2E, butthey are simple and less complicated. The vesicula seminalisis an undivided elongated oval sac (fig. 3), measuring "2 by•04 mm. It is not in the slightest degree convoluted. It issurrounded on all sides by the cells of the prostate glands,except towards the posterior end, where it is contiguous withthe wall of the cirrus-pouch. The length of the ductusbetween the vesicula and the pars prostatica is about "15 mm.For the first two thirds of that length it has a diameter of"015 mm.; it then somewhat suddenly widens to "023 mm.,which diameter it retains till it passes into the pars prostatica.The latter has a length of '05 mm., and a maximum diameterof '035. mm. It has a globose shape, and into it open theducts of the numerous prostatic .cells. These are entirelyconfined to the part of the cirrus-pouch behind the parsprostatica, so that their ducts all pass forward. They arelarge tear-shaped cells elongated in the long axis of thecirrus-pouch, and having an average size of "027 by "012mm. Their outline may be more or less quadrilateral owingto compression. They stain deep purple with hteinalum-eosiii,and have distinct round, rather small (-004-"005) nuclei.The terminal part of the ductus ejaculatorius, which, althoughnot extended in any of my specimens, functions as an ex-sertilecirrus, is slightly convoluted. As a rule it describes onlyone turn, a little in front of the pars prostatica, but itsposition is not constant. The length of this part is about "1mm. and its diameter is •02-"025 mm. Between this part andthe wall of the cirrus-pouch are numerous small, round cells.

412 WILLIAM N1C0LL.

These are obviously not prostatic cells, for they present adifferent appearance and take on a distinctly, blue stain.Moreover, ducts cannot be made out. Various functionshave been ascribed to these cells. Most frequently they haveeither not been noted or considered to be prostatic cells.They have also been regarded as glands opening into theductus ejaculatorius. Neither of these theories has beenverified. The staining reaction differentiates them from theprostate cells and from similar cells, e . g . those of the shell-gland. On the other hand, they bear a distinct resemblanceto the circum-cesophageal and peri-vaginal cells, as also to the"subcutaueous gland cells" ( i . e . myoblasts). The resem-blance to the circum-cesophageal cells, which Bettendorf1 hasshown to be the myoblasts of the qesophageal muscle-fibres,suggests that the cells surrounding the ductus ejaculatorius,as also the peri-vaginal cells, are the myoblasts of the muscle-fibres of the walls of these structures.

The ovary is an almost globular body situated close behindthe ventral sucker and a considerable distance in front of theanterior testis. I t may lie on either side of the middle line,or, according to Olsson, it may be median. In none of myspecimens did it occur in the latter position; it was mostfrequently on the left side. The size is '23 by *19 mm., thethickness "16 mm. The configuration of the shell-glandcomplex has already been carefully described by Blanchard.Just behind the ovary lies a small oval receptaculum semmis.From its inner side there arises a duct giving off Laurer'scanal, which is a straight tube of moderate length, and thenrunning forwards to join the oviduct. The latter issues fromthe inner surface of the ovary, and passes backwards. Afterbeing joined by the duct from the receptaculum seminis, itturns forwards to pass into the ootype, and thence into theuterus. Blanchard's representation of the shell-gland issomewhat diagrammatic. I t is much more extensive and isnot enclosed within a membrane. I t lies under the dorsal

1 " TJber Muskulatur imd Sinnezellen der Trematoden," ' Zool. Jahrb.Anat.,' x (1897).

STUDIES ON THE D1GKNET10 TREMATODES. 413

surface of the body, and consists of a large number of smallcells closely aggregated and composing a fairly distinct bodyto external view.

The common yolk-duct joins the oviduct between theentrance of the dnctus receptaculi and the ootype. The yolkreservoir lies just behind the shell-gland and is median. Itforms a more definite swelliug than Blanchard iudicates. It,is formed by the junction of the two transverse yolk-ducts.The longitudinal ducts run parallel to the intestinal diverticulaand along their ventral surface. The yolk-glands consist oftwo lateral groups of follicles extending continuously fromthe level oE the pharynx to the posterior end of the body.Behind the posterior testis they extend in towards the middleline and fill up the posterior part of the body. In additionoffshoots are sent in between the testes and in front of theanterior testis, and these almost unite in the middle line,thus separating the testes from each other and from theuterus. There is no tendency towards proliferation in frontof the ventral sucker, the lateral fringes having a fairly con-stant width. Their situation is particularly towards theventral surface, so that laterally they lie ventral to theintestinal divevticula and posteriorly they do not approachthe dorsal surface to any great extent. The follicles areirregularly ovoid and measure "08—'10 by "04—"06 mm. Bachcontains about a dozen gland cells, which present two distinctappearances. In each follicle there is almost invariably onecell situated centrally (fig. 4) differing from the surroundingcells in shape and staining reaction. Tins central cellappears to be free, not much compressed by the neighbouringcells, and in consequence has a regular oval outline. Theremaining cells are closely pressed together into variouspolyhedral shapes. The staining reaction is more distinctive.The stain used was weak hasmalum with aqueous eosin, butcorresponding results were obtained with combinations ofhaernatoxylin, methylene blue, and saffranin. The peripheralcells take on a uniform purple colour, while the central cellappears pink with a circumferential granular zone. The nuclei

414 WILLIAM N1C0LL.

also differ. In the peripheral cells they appear to consistof tlu*ee concentric layers. The outmost zone is granularand stains deep blue, the middle is white, wjiile the centralpart, the nucleolus, stains bright red. In the central cell, onthe other hand, the nucleus stains uniformly bright red andappears to consist of little more than the nucleolus. Thecells measure 02-"03 mm. in diameter, while the nucleimeasure '006—"0075 mm., but those of the peripheral cellsappear to be slightly larger than that of the central cell.The central cell is obviously the most mature part of thefollicle, and it is probable that only in this condition are theyolk-cells despatched from the follicles. The yolk-ducts andreservoir, at any rate, contain ouly such cells. In theirpassage down, the yolk-ducts they are compressed into acubical or short cylindrical shape; in the reservoir theybecome polyhedral, but they again become cubical on passinginto the common yolk-duct. They i-etain their bright rednuclei throughout, and these are still conspicuous within themost mature ova. No intrinsic muscle-fibres or true epithe-lium of the yolk-follicles or yolk-ducts could be observed, butthis does not prove their absence as they are particularlydifficult to demonstrate.

Turning back from the ootype the uterus describes amoderate number of convolutions in the space between theposterior border of the ventral sucker and the anterior borderof the anterior testis. Laterally it is confined by theiutestinal diverticula. Owing to its thickness the ovaryis not overlapped by the uterus. The convolutions tendtowards and cause bulging of the ventral surface of the body.The terminal part of the uterus runs straight forward on theright side of the cirrus-pouch and passes into the vagina atthe level of the posterior end of the pouch. The vagina isalso straight and has the usual muscular structure. I tsdiameter is '019 mm. in the uudilated condition. Thecuticular lining is "004 mm. thick. The thickness of thecombined muscular layers is '003 mm. and the diameter of thelumen is only *005 mm. To admit the passage of the ova it

STUDIES ON THE D1GBNBTIC TREMATODES. 415

must therefore be capable of considerable dilatation I t issurrounded by lax connective tissue, in which are embeddedthe peri-vaginal cells already referred to.

The ova are usually less than 100 in number. The shapeis ovoid, slightly blunter at the opercular pole. The shell is"0018 mm.' thick and bright yellow, not darkening muchthroughout the uterus. The size of the ova is "OTS-'OSO by•040—"044 mm.; this is somewhat larger than the size quotedby Olsson, but agrees closely with that of Liuton. There isabsolutely no intra-uterine segmentation, the ovarian ovumremaining undivided till deposition. The yolk-cells withinthe egg also remain unchanged, and can be easily distin-guished from the ovarian cell by their bright red nuclei, thenucleus of the ovarian cell taking on a darker, nearly purplecolour with hsemalum-eosin.

Olsson's figure (PI. IV, fig. 52) gives a somewhat erroneousimpression of the appearance of the ova and uterus in aspecimen of average size. The ova are usually propor-tionately larger and the convolutions of the uterus areindistinguishable.1

Systematic position of Distomum laureatum Zeder.The inclusion of this species within the sub-geuus Crosso-

d era by Dujardin in 1845 need not be discussed here. Themost recent attempt to define its systematic position is thatby Braun,2 and his classification is accepted by Looss,3

Heymann,4 Pratt5 and Stafford6. Braun included it in a newgenus, Crepidostomum, of which the type is C. metcecus(Bru.) from bats. The two species are certainly very nearly

1 In the two specimens from Olsson's collection which I examinedthe uterus does not have the disposition represented by Olsson. Theova are congregated more over the doi-sal surface of the ventral sucker,so that they ai-e best seen on viewing the animal from the dorsal surface.

- ' Annal Hofmusevim, Wien,' xv (1900), p. 232.3 • Zool. Jahrb. Abth. Syst.,' xvi (1902), p. 453.4'Ibid.,'xxii (1905), p. 97.5 ' American Naturalist,' xxxvi, p. 957.r> ' Zool. Anzeiger,' xxvii, p. 490.

416 WILLIAM N1C0LL.

related, but in my opinion D. l au rea tum does not belong tothe genus of which D. metoecus is the type. The widelydifferent hosts might in the first place raise doubt as to theclose relationship of the two forms, although, as Braunremarks, too great weight need not be attached to this,because the larval stages of both may be passed through ininsect larvae forming food common to bats and fishes. Wemay therefore neglect this.

The close resemblance between the two species, however,is not borne out on more detailed examination. Severalimportant features of difference are apparent. The first, andpossibly the chief of these, is the condition of the circum-oralswelling and papillae. Braun did not fail to notice thedifference here, but he under-estimated its importance. InOrepidostomum metoecusthe circum-oral collar is confinedalmost entirely to the dorsal surface of the sucker. It doesnot extend on to the ventral surface, and thus its edges areat some distance from the aperture of the sucker. In Dist .l anrea tum the collar completely encircles the sucker and itsedges are contiguous with, or even project into, the aperture.There are thus no ventral papillae in C. metoecus, all beingdorsal, or at most two being dorso-lateral. Further, they areonly five in number as opposed to six in D. l aurea tum.Braun's attempt to correlate the discrepancy is certainlyingenious, and possibly explains to some extent the origin ofthe papillae and the increase in their number. He. considersthat the median dorsal papilla in C. metoecus which isfurcate (zweizipfelig), must be regarded as a double papilla,and as such is equivalent to the two dorsal papillae of D.laurea tum. The division of this median papilla wouldcertainly make the number six, but unfortunately Braunignores the fact that (from his own description, p. 230) thetwo neighbouring papillae are not altogether simple, butappear to approach the middle papilla in shape, i . e . to betwo-pointed or bi-partite. These have equal claim to beregarded as " Doppelpapillen," and in this way the numberwould be eight. There is no evidence of such splitting of

STUDIKS ON THE D1GKNETIO TBEMATODES. 417

the papillae in Dist. laureatum. On the strength of theforegoing alone I should be inclined to exclude Dist.laureatum from the genus Crepidostomum, for it isobvious that there is a wide interval of development betweena condition of six and a corresponding condition of fivepapillae, even although one or more of the latter is in theprocess of division. Further differences of generic impor-tance are, however, not difficult to seek. The first of theseis to be found in the position of the genital aperture. InBraun's figure it appears midway between the ventral suckerand the pharynx, and he describes it as close in front of theanterior border of the sucker. It is therefore considerablyfurther back than in Dist. laureatum.1 It appears single inBraun's figm-e. The cirrus-pouch is of great length, extend-ing beyond the ventral sucker by nearly half the diameter ofthe latter. In Dist. laureatum it barely reaches the centreof the sucker. Braun does not offer any details of theinternal structure of the pouch. A noticeable feature inCrepidostomum metoecus is the enormous size of thetestes, each being much larger than the ventral sucker, andtheir appi-oximation to the posterior end of the body. Thiscannot be regarded as of very great importance. Of greatermoment is the position of the ovary and the condition of theuterus. In Crepid. nietceeus the ovary lies not far infront of the anterior testis, on the right side of the body andseparated from the ventral sticker by the cirrus-pouch.Braun makes no mention of amphitypy, although he hadnumerous specimens. The uterus is practically minimal inlength and contains not more than two or three ova, whichare much smaller ("055 mm.) and broader than those of D.laureatum. Other features of difference are the nearlyequal suckers, the somewhat small, round ventral sucker,and the absence of pre-pharynx and oesophagus in Crepido-

1 I may be hei'e accused of inconsistency in admitting the correctnessof Braun's observation while doubting that of Olsson ; but the justifica-tion lies inthefact that many errors have beenfound throughout Olsson'swork, whereas Braun's observations are, as a rule, beyond dispute.

418 WILLIAM NICOLL.

stornum rnetcecus, but the last mentioned is of littleimportance, for, as Braun remarked, a short oesophagus maybe present as also a pre-pharynx.

The features of primary diagnostic importance are, there-fore, the circum-oral collar and papillas, the position of thegenital aperture, the length of the cirrus-pouch, and theextent of the uterus with the number and size of the ova; ofsecondary importance are the large testes, the nearly equalsuckers, and possibly the position of the ovary in Crep id .metoecus. That these are of much greater than merelyspecific importance can hardly be denied, and it follows thatDis t . l au rea tum Zed., cannot be included in the genusCrepidos tomum Braun. From the genus A c r o d a c t y l aStafford1 it differs in having the ventral sucker considerablylarger than the oral sucker, the rather short cirrus-pouch,and apparently the ventral papillae not so pronounced. Thestructure of the cirrus-pouch in A c r o d a c t y l a is notmentioned, but it is presumably muscular. From the generaBnnode ra Raill. and Pa tag iun i Heymann it is suffi-ciently distinguished by the structure of the cirrus-pouch,the extent of the uterus, and other features to which I shallrefer later. In short, it must be regarded as the type of adistinct genus, for which I propose the name S t ephano -phia la , with the following- provisional definition :

Body of medium size, elongated, flattened. Cuticleunarmed. Suckers fairly muscular, the ventral sucker beinglarger than the oral sucker, and situated on the border ofthe first and second thirds of the body-length. Oral suckersubterminal, with its anterior part swollen and surrouudedby a row of six equal, muscular, contractile papillas, arisingfrom the muscle-substance of the sucker, two being ventraland four dorsal. Intestine with short pre-pharynx, medium -sized pharynx, short oesophagus, and diverticula extendingto hind end of body. Excretory vesicle simple. Genitalaperture median, midway between suckers. Sinus genitalisabsent or rudimentary. Cirrus-pouch with muscular walls

1 ' Zool. Anzeiger,' xxvii, p. 491.

STUDIES ON TflJS D1GENBTIC TREMATODES. 419

not extending much, if at all, beyond the ventral sucker.Vesicula seminalis simple; ductus ejaculatorius only slightlyconvoluted; distinct pars prostatica; prostatic cells fairlynumerous. Vagina of no great length. Testes, two, rounded,close behind each other, about midway between ventral suckerand posterior end of body. Ovary rounded, not far behindventi-al sucker, and separated from the testes by part of theuterus, which is of moderate leugth, confined between ventralsucker and antei-ior testis. Yolk-glands lateral, extendingneai'ly the whole length of the body and uniting behindtestes. Receptaculum seminis and Laurer's canal present.Ova not vei-y numerous, measuring about "075 X "04 mm.No intra-uterine segmentation.

Type: St. Laureata (Zeder). Includes also St. t r ans -marina n. sp. [= Crepidostomum laureatum (Zed.)Stafford, 1904], and probably two other undescribed Americanforms (see p. 35).

With regard to the systematic position of the genus itprobably lies nearer Acrodactyla than Orepidostomum.From Bunodera, Pat.agium, Rhytidodes and othersit is much further removed. Heymann has already discussedthe relationship of the genus Crepidostomum to Buno-dera and Patagium. The somewhat scanty knowledge ofthe first-named genus did not appear to offer any seriousobstacle to the inclusion of these three geuera under the sub-family BUNODERIN ;, and, in addition, the importance of therecognised features of difference was under-estimated, as willbe evident from what follows.

The presence of circum-oral swellings or papillae being arare and peculiar occurrence amongst Distomids, the mostnatural conclusion is that they must have been evolved fromsome simpler type. That they bear no analogy to the muchcommoner collar of cephalic spines of the ECHINOSIOMINJJ; andother forms has already been amply demonstrated by Looss,and needs no further discussion here. The resemblance,however, in the internal anatomy of the genera under con-sideration, especially of Stephanophiala, to the ALLO-

420 WILLIAM NICOLL.

CREADIINJE and allied forms has previously been remarked onby more than one author, and there is certainly no otherknown group to which they seem so closely connected.B u n o d e r a and P a t a g i u m , nevertheless, divei-ge widelyfrom the ALLOCREADIIKS: in several respects. On the otherhand, were it not for the circum-oral papillce, S t e p h a n o -p h i a l a l a u r e a t a might be regarded as an Allocread.

From the point of view of the circum-oral collar, the generaP a t a g i u m and R h y t i d o d e s Lss. show the most primitivecondition of a simple swelling of the muscle-substance of thesucker with commencing differentiation. The next stage,considerably removed, is that of C r e p i d o s t o m u m in whichpapillae have appeared, showing a tendency to further sub-division, and the most advanced stage is that of S t e p h a n o -p h i a l a , B u n o d e r a and A c r o d a c t y l a , in each of whichthe condition is very similar, although, as I have ti'ied toshow, they may not be the direct evolutionary products offorms such as C r e p i d o s t o m u m , but may have proceededalong independent lines, the intermediate members of whichhave been lost or are not yet known. A consideration of theinternal anatomy leaves hardly a doubt of this, for S t e p h a n o -p h i a l a and B u n o d e r a differ very much, while the formerapproaches C r e p i d o s t o m u m and the latter P a t a g i u m .

From a detailed examination of the internal structures it isevident that S t e p h a n o p h i a l a closely resembles the ALLO-CREADIHOJ: in its most essential features, viz. the position of thegenital aperture, the structure of the cirrus-pouch and itscontents, the position of the testes, the extent and situationof the uterus, and the condition, size and number of the ova.This appears to have been noticed by Pratt1 who includedC r e p i d o s t o m u m Brn. in a sub-family, PsiLOSTOMiNiK Pratt,comprising A l l o c r e a d i u m and several allied genera,3 while

1 ' American Naturalist,' xxxvi, p. 8SS.- Pratt is rather inconsistent, for on p. 896 he notes : " Yolk-glands

do not extend in front of acetabulum " as a feature of the sub-familyPsn.osTOMiN.ffi:, while just above he has—" Yolk-glands extend in frontof acetabulum," under which sub-division he puts Oalycodes lies.,

STUDIES ON THE DIGBNETIO TREMATODES. 421

Bunode ra is relegated to a sepai*ate sab-family, BUNODERIN.8:Pratt, including the rather anomalous genus Te rges t i aStoss.

In Crepidostornum the uterus appears to have under-gone a process of retrogression or degeneration, whileBunodera , and, to a less degree, P a t a g i u m display a con-dition altogether foreign to the ALLOCEEADIIN^!, in which theuterus never extends beyond the anterior border of the firsttestis. In Crep idos tomum and Acrodac ty l a the structureof the cirrus-pouch is not well known, but indications pointto its being not unlike that of S t e p h a n o p h i a l a . Buno-de ra and P a t a g i u m again display a distinctly differenttype, with non-muscular wall and more or less highly-convoluted vesicnla seminalis. The absence of muscle-fibresmight be regarded as the result of a series of degenerativechanges, but that is merely hypothetical. Further, inB u n o d e r a the condition of the ova, in which a Mira-cidium lai'va is developed within the uterus, is very dis-similar from that of the ALLOCREADIIN^; and S t e p h a n o -phia la . Iu C r e p i d o s t o m u m and P a t a g i u m the conditionof the ova is not known.

The inclusion, therefore, of all these genera within thesub-family, BUNODERIN2E, as proposed by Looss and Hey maun,is not without objection. They are possibly related, but howclosely is not very apparent. Too great weight has hithertobeen placed on their common possession of a circum-oralcollar, aud, as in the case of R h y t i d o d e s , such a structuremay be present in a genus which cannot be included in thesame sub-family. To consider the circum-oral collar as t hediagnostic feature of the sub-family BUNODERIN-E would bea reversion to the now discarded system of classification byexternal characters. We must therefore look to the internalstructure, mainly, for guidance. From this it is evident

Crepidostomum Bi-n. andHelicometraOdlm., although be includesthose genera in his sub-family. Pratt's classification is obviouslypremature but it is of great help, and lie is certainly correct in separa-ting Bunodera from the PSILOSTOMIIOS.

422 WILLIAM NICOLL.

that a somewhat broad line of separation exists betweenStephanophiala , Acrodactyla and Crepidostomum onthe one hand and Bunodera and Patagium on the other.It is unfortunate that more details are not available in thecase of Crepidostomum, Acrodactyla, and Patagium,but from what is actually known it is highly probable thatthey display all the features mentioned in the followingtable:

Stephanophiala (Crepido-stomum and Acrodactyla ?).

. Directly tandem. Confined between ventral

sucker and anterior testis

1. Testes2. Uterus

3. Cirrus-pouch

4. Ova

Musculai*; vesicula seminalisand ductus only slightlyconvoluted

No intra-uterine segmentation.

Bunodera (andPatagium).

ObliqueExtending beyond

testes, and evenfilling up pos-terior part ofbody.

Membranous (non-nauscular); vesi-cula and ductushighly convo-luted.

M i r a c i d i n mlarva developedwithin uterus.

The difficulty again arises as to the precise importance tobe attached to these differences in structure. From a studyof the methods of classification propounded and developedby Looss I take it that the condition of the ova and thecirrus-pouch are of extreme importance, and that generadiffering in two such essential features can hardly beincluded in the same sub-family. On examination of alreadyexisting and strictly demarcated sub-families it will be foundthat no such divergence in structure is to be met with.Amongst such sub-families, for example, as the ECHINO-STOMIN*, ALLOCREADHN.S: or GORGODEKIM; with their com-paratively numerous members no such difference in structurewould be admitted. From these considerations, therefore, itseems advisable to separate the genera Stephanophialaand Crepidostomum from the sub-family BUNODJEEINA1,

STUDIES ON THE DIGRNKTIC TRBMATODES. 423

and to establish for them a distinct sub-family for which Ipropose the name STEPHANOPH/ALTN ; n. snbfam., with thefollowing provisional diagnosis.

Small to under middle-sized forms with fairly muscularbody, the anterior part of which is capable of considerableextension. Cuticle without spines or scales. Suckers mus-cular and of moderate size, the ventral sucker being situatedat the end of the anterior third of the body or somewhatfurther back. Oral sucker with a circum-oral collar developedfrom the muscle substance of; the sucker, from which anumber (five or six) of small tentacular papillee arise. Intestinewith very short pre-pharynx, muscular pharynx, shortoesophagus, and long simple diverticula extending to posteriorend of body. Genital aperture median, between the suckers.Sinus genitalis small or vestigial. Cirrus-pouch elongated,with muscular walls. Vesicula seminalis and ductus ejacula-torius simple and not much convoluted. Testes two, simple,median in the middle of the post-acetabular region. Ovarysimple, rounded, not far'behind ventral sucker and separatedfrom testis by part of uterus. Receptaculum seminis andLaurer's canal present. Yolk-glands mainly lateral, extensive.Uterus confined between anterior testis and ventral sucker.Vagina simple, short. Ova not numerous, measuring about'05—"08 mm. No intra-uterine segmentation.

Type: Stephanophiala Mihi. Iucluding also probablyCrepidostomum Brn., and very doubtfully AcrodactylaStafford.

As a result of this separation Heymann's definition of thesub-family BONODEBIN.*: LSS. requires modification. The sub-family must for- the present be restricted to the generaBunodera and Patagium, and it is obvious that thesegenera differ from each other much more than Crepido-stomum and Acrodactyla do from Stephanophiala , notonly as regards the circum-oral collar but also in respect ofthe internal structure. The modifications, as already indicated,are: Suckers nearly equal; testes oblique; uterus extending

VOL. 53 , PART 3. NEW SEMES. 30

424 WILLIAM NICOLL.

beyond the testes; terminal part of male genital apparatusenclosed within a non-muscular pouch; vesicnla seminalisconvoluted; ovary immediately behind ventral sucker andseparated from testes by considerable part of uterus; ovacontain a M i r a c i d i u m larva before deposition. Length•08--10 mm.

Type: B u n o d e r a Raill.

In addition to the species hitherto mentioned there areseveral other forms, mostly from America, which possess arow of circum-oral papillas. Two of those, D i s t o m u m aur i -c u l a t u m Wedl. and D . p e t a l o s u m Lander, were regardedby Looss1 as probable members of the genus B u n o d e r aStafford,3 however, differentiated D. p e t a l o s u m Lander( = D. a u r i c u l a t u m Wedl. Linton) from B u n o d e r a , andproposed it as type of the new genus A c r o d a c t y l a . Thechief features of this genus, according to Stafford, are thelarge ventral oral papillas, the position of the genitalaperture, and the large cirrus-pouch. To these I should addthe fact that the ventral sucker is smaller than the oral. Thestructure of the cirrus-pouch and the condition of the ova arenot noted. The limited extent oE the uterus indicates thatthis genus is more nearly related to S t e p h a n o p h i a l a andC r e p i d o s t o m u m than to B u n o d e r a , and I have includedit provisionally within the sub-family STEPHANOI?HIALIN2E.

With regard to the American forms of D i s to rauml a n r e a t u m described by Linton and Stafford, it is doubt-ful if they are really identical with the European variety. Theonly differences which I can detect in Linton's specimens arethe backward position of the ovary and the slightly reducednumber of ova. In Olsson's figure of the species, however,the ovary is a little distance behind the ventral sucker, so thatthis variation may occur in the European form. The smallernumber of ova may be only a seasonal variation. Lintonmakes no mention of the cirrus-pouch, but Stafford says it

1 ' Zool. Jahrb. Syst.,' xvi, p. 453.= ' Zool. Anzeiger' (1904), xxvi, p. 491.

STUDIES 0NT THE DIGEtfETIC TRBMATODES. 425

extends beyond the ventral sucker. The latter also describesthe ovary as midway between ventral sucker and anteriortestis,and the ova as not numerous—ten to twenty. In this caseit is apparent that a different species is under consideration,for in the European form, according to Olsson's observation,which I confirm, the cirrus-pouch does not extend beyond thecentre of the ventral sucker. For this American species Ipropose the name S t e p h a n o p h i a l a t r a n s m a r i n a ( =Orep idos tomum l a u r e a t u m Stafford, 1904, = ?Dis-tomum l a u r e a t u m Linton, 1893) from S a l v e l i n u s font i -na l i s Mit. and Sal mo mykiss .

Stafford mentions two other varieties, one from P e r e af l avesceus , the other from N e c t u r n s m a c u l a t u s , andthese will possibly prove to be further species of the genusS t e p h a n o p h i a l a . With regard to Crepidos toniu inco rnu tum (Osborn),1 it is doubtful if this species can beincluded in the genus S t e p h a n o p h i a l a . The small size ofthe ventral sucker is against this and brings it into closerrelation with A c r o d a c t y l a . The species, however, is notyet sufficiently well known for its position to be determined.If it cannot be included in the genus A c r o d a c t y l a it mayrequire to be considered as the type of a distinct genus.

The natural sequel to the foregoing classification would bethe formation of a family BUNODEKIMS along the lines indicatedby Heymann in his definition of the sub-family BtJNODEBiNJi:,but such a step would be undoubtedly premature, if noterroneous. I t must be regarded as very doubtful if theSTEPHANOPHIALINJ: are so closely related to the BONODEKIN*,as has been hitherto considered. Most indications seem topoint to a further separation of these two sub-families, anda nearer approximation of the STEPHANOPHIALIN^; to theALLOCREADIIM;. This, however, must be a matter for futuredetermination.

1 ' Science,' xv (1902), p. 573.

426 WILLIAM N1C0LL.

Sub-family BRACHYCLADIIN55 Odh., 1904.

Genus Brachyc lad ium Lss., 1899.

Brachyc lad ium oblongum (Braun). PL 9, figs. 6—9.

? = Oampula o b l o n g a Cobbold.1900. Campula ob longa Cobb. Braun, ' Centralbl. f.

Bakter./ xxviii; ' Abtheil./ i, pp. 249-255, 3 figs.1902. B rachyc l ad ium ob longum (Brn.), Looss, fZool.

Jahrb. Abth. Syst.,' xvi, pp. 707-717 and 775-778.1904. B rachyc l ad ium oblongum Odhner, 'Die Trema-

toden des arktischen Gebietes, Fauna Arctica,' iv, p. 347.This species has been the cause of much systematic dis-

cussion, and its ultimate fate may be regarded as a criticaltest of the priority law as applied to zoological nomenclature.The root of the trouble lies in the fact that Cobbold's typespecimens of Campula ob longa have been lost or destroyed,and that his description1 of the species is inadequate todifferentiate it from allied and more recently discoveredspecies. I have made an exhaustive but fruitless search forCobbold's specimens, and it may certainly be considered thatthey no longer exist, unless, perchance, in some privatecollection. What remains to us, therefore, of Cobbold'sspecies is merely his scanty description, which, as Loossjustly remarks, is of no value whatsoever for diagnosticpurposes. Braun's identification, as Campula oblongaCobb., of a species which he found in the same situation inthe same host as Cobbold found his specimens, is regardedby Looss as inadmissible, and his opinion is seconded byOdhner. Braun defended his diagnosis on the grouud of thesimilarity of habitat and the manifest resemblance betweenhis specimens and Cobbold's description and figure so far asthey went, but Looss pointed out that Brachyc lad iumpa l l i a tum Lss., Br . r o c h e b r u n i Poir., and Br . de lph in iPoir. resemble Cobbold's Campula oblonga just as closelyas do Braun's specimens, and so might just as readily be

1 ' Trans. Linn. Soc. Lond.,' xxii (1858), p. 168, PI. XXXIII, figs. 84, 85.

STUDIES ON THE DIGENETiO TREMATODES. 427

regarded as Oampula oblonga. The obvious outcome ofthis is that Campula oblonga Cobbold must be considereda nomen nudum, and that Braun's specimens must bere-named Brachycladium oblongum (Braun). lam ableto offer a justification, in part, of Looss's conclusions, for ina female porpoise which I have recently (August, 1908)examined I found in the bile-ducts, in addition to numerousexamples of Brachycladium oblongum (Brn.), a singlespecimen of another Trernatode. This was accidentally dis-covered on washing the parasites, and, in spite of furtherrepeated search no more specimens could be obtained. Itwas easily differentiated from Brachycladium oblongumby its deep red colour, more elongated body, and the apparentabsence of spines. I have not yet identified this specimen, butit appears to be a species of Brachycladium. This speciescould not possibly have been the one Cobbold found, but itsoccurrence shows that more than one Trematode species mayhave as its habitat the bile-ducts of Phocsena communis.

The first specimens which I had the opportunity of examin-ing formed part of Professor Mclntosh's collection, and wereobtained by him from the liver of a porpoise shot in Loch-maddy (North-West of Scotland) in April, 1865. About fiftyexamples were found, and they were identified by ProfessorMclntosh at that time as Campula oblonga Cobbold. Asalready mentioned I have obtained the same parasite myselffrom one of two porpoises captured in the Firth of Clyde,near Millport. The first of these, a young male, was unaffected,but in the second, one of the lobes of the liver contained morethan a hundred specimens. The presence of the parasites inthe liver was indicated by large yellowish prominences on itssurface, which felt extremely hard. The same stony hardnesscould be felt throughout the substance of the affected lobe.On opening into it the biliary canals were found lined with athick layer of dense fibrous tissue. The terminal parts of thecanals were usually dilated to form small sacs, in which largenumbers of the parasite were closely packed together. Thesewere, however, easily pressed out, Detailed examination has

428 WILLTAM NICOLL.

shown these specimens to be identical with the speciesdescribed by Braun, or, at most, to differ very slightly fromit. Braun's description deals only with the more obviousanatomical features, and I propose here to describe thestructure in fuller detail. Looss has already 1 given a fairlyexhaustive account of the anatomy of B r a c h y c l a d i u mp a l l i a t u m , and it may be of interest to see in how far hisresults are borne out by my observations.

The specimens obtained from Lochmaddy were well pre-served in alcohol and most of them were in a moderate stateof extension, although few were so greatly extended as thespecimen shown in Braun's fig. 3. The most general lengthwas 5-6 mm., and the breadth of the specimens was 2-2*5 mm.,i . e . the length is about two and a half times the bi-eadth. Myown specimens are more extended. Many of them reached 7mm. in length, and the length was three to three and a halftimes the breadth. This agrees with Brauu's observations.

The other B r a c h y c l a d i u m spp . are much more elongatedthan this, the length being in the case of Br. r o c h e b r u n iten times the breadth, while in Bv. p a l l i a t u m it is five or sixtimes. The greatest thickness in my specimens was #75--85mm. The outline is broadly lanceolate, being somewhatpointed at each end. The greatest breadth occurs justbehind the ventral sucker, the greatest thickness at the levelof the genital aperture.

The whole body is covered with a thick cuticle, vaiyingfrom '008—'013 mm. in thickness, but not in any uniformmanner, thicker and thinner parts alternating with each other,and there being no difference in this respect between ventraland dorsal surfaces. The cuticle is much thinner than thatof Br. p a l l i a t u m . Strong spines stud the entire surface ofthe body, being present right to the posterior end, and evenin a small depression on which the excretory vesicle opens.As usual they vary much in size, the largest spines beingfound about the thickest part of the body and the size gradu-

1 ' Beitriige z. Kenntnis der Trematoden. Zeitschr. f. wissen. Zoolog.,'xli (1885), pp. 390-427, figs. 1-14 and 30.

STUDIES ON THE DrGENETIO TRKMATODES. 429

ally diminishing forwards and backwards. Arouud the oralsticker they are "019 mm. long with a base measurement of•0045 mm. The maximum size about the middle of the bodyis "058 by '014 mm. Towards the posterior end they measure•037 by "012 mm. They are thus much shorter than the spinesof Br. palliatum. The spines are deeply embedded in thecuticle, penetrating its wliole thickness and causing bulgingof the basement membrane. Immediately beneath the latterlie the usual three layers of muscle-fibres. The circular fibreshave a diameter of "0019 mm., and are separated by spacesequal to their diameter. The longitudinal fibres measure•003--004 mm., and are separated by spaces of "OOG-'Ol mm.The diagonal fibres measure 0035-"0055 mm., and are widelyseparated by spaces of #04 mm. Those passing in oppositedii-ections make an angle of 125° with each other, but thisvaries with the state of contraction, The longitudinal anddiagonal fibres run for the most part in pairs, which are inmore or less intimate contact. Sometimes they are indistin-guishable ; sometimes a distiuct interval separates them.This corresponds with the condition described by Looss inBr. palliatum. In both species the circular fibres run singly.. The suckers are small in comparison with the size of the

animal. Both are globular with circular apertures, andpresent no peculiar feature. The oral sucker is subterminaland has a diameter of "33 mm. The ventral sucker issituated at a distance of rather more than a quarter of thebody length from the anterior end, and hns a diameter of•43—'46 mm. The diameters are therefore in the propor»tion of 3 : 4, and are respectively about one sixteenth and onetwelfth of the body length (taking the average as 5'5 mm.).This agrees fairly well with Braun's measurements.

The radial fibres of the oral sucker are '015 mm. thick ;tliose of the ventral sucker "025 mm., the circular fibres about•019 mm. The wall of the oral sucker has a thickness of•078 mm., that of the ventral sucker '09 mm. The cuticularlining of the suckers is thinner than the cuticle covering thebody, being only about "004 min. thick.

430 WILLTAM NICOLL.

The mouth opens into a short but wide pre-pharynx.From the ventral side of this there arises a well-mai%kedpre-pharyngeal diverticulum (fig. 8), which passes back-wards ventral to the pharynx, and may extend a shortdistance beyond it. This diverticulum forms part of the pre-pharynx and there is no difference in. its structure; itsoccurrence, however, is constant. Such a structure appearsto be absent in Br. p a l l i a t u m , and was not observed byBraun or Poirier. Its function is not very apparent, but itis a curious fact that in each of three specimens which Iexamined a number of ova were found in the diverticulum.Ova, however, were found in one case in the intestinaldiverticula, and were probably accidentally swallowed. Thewidth of this pre-pharyngeal.pouch is "13—"18 nim., but at itsjunction with the pre-pharynx it is only -09 mm. Its wallsare in some cases thrown into irregular folds, but they arenot muscular.

The pharynx is somewhat flask-shaped, narrowest in frontand with its anterior end projecting far into the pre-pharynx.The extreme freedom of movement of the pharynx is evidentfrom the fact that its anterior end may be. found directedventrally, dorsally or towards either side. I ts length in a5'5 mm. specimen is "36 mm. ; breadth "22 mm. and thickness20 mm. It is, therefore, a comparatively large structure, and

is narrower than that o£ Br. p a l l i a t u r n and larger inproportion to the size of the animal. The histologicalstructure is the same as that of the suckers. The myoblastsmeasure "008-"011 mm., with minute reddish eccentricnucleoli.

The oesophagus arises from the posterior end of thepharynx as a narrow tube, transversely oval in section, witha diameter of '10 mm. I t gradually increases in diameter to•13 mm., where, at a distance of *05 mm. behind the pharynx,there is a small dilatation on the left which causes the widthto increase to "20 mm. The bifucation takes place at adistance of '115 mm. behind the pharynx. This, however, isnot a bifurcation in the usual sense of the term, when the

STUDIES ON THE Dl GENET JO TBEMATODES. 431

diverticula separate from each other at a somewhat wideangle ; it is rather a division of the oesophagus into two by athin septum. The two parts run side by side and theirlumen is still lined with " cuticle." Intestinal epitheliumdoes not appear till a further distance of OS mm., and imme-diately thereafter the diverticula proper arise. This struc-tural peculiarity of the oesophagus has not been noted byany previous author and is not indicated in Brann's figures.It is probable, however, that the small transverse parts inBr. palliatum and the other two species, joining theundivided oesophagus to the main diverticula correspondwith the parts which I have described above, and that theyare lined by cuticle and therefore functionally part of theoesophagus. Around the anterior end of the oesophagus areseveral groups of rather large cells, which probably corre-spond to the salivary glands of Br. palliatum as describedby Looss.

The diverticula occupy the lateral fields midway betweendorsal and ventral surfaces and extend to within a shortdistance of the posterior end of the body, turning in towardsthe middle line at their termination. In addition to the maindiverticula a pair of smaller diverticula, one on each side, passforwards and reach almost the level of the middle of the oralsucker. These secondary diverticula are distinctive of thegenus. The condition of the diverticula does not differ fromthat in the other species. They pursue a very erratic course,and numerous dilatations of various sizes, never attaining thesize of twigs, are found both on their outer and inner sides.The sinuosities are so numerous and irregular that on sectionthe diverticula present the appeai'ance of being traversed bytrabeculae. The condition suggests that the diverticula,originally simple, had grown too long for the body and hadbecome at first regularly sinuate and then crushed up to beaccommodated in the limited space.

The structure of the intestinal wall is identical with thatdescribed by Looss. The epithelium is well developed andpresents numerous villus-like projections. The muscular

432 WILLIAM N1C0LL.

coats of the oesophagus are well marked but those of thediverticula are thin.

As already noted the excretory aperture opens on a largepit-like depression at the posterior end of the body;whether this depression is au intrinsic part of the excretorysystem or not I am at a loss to say. Small cuticular spinespenetrate a short distance within it, and the rest of its surfaceis lined by a thin membrane which appears like cuticle but ismuch thinner than the body cuticle. It may be either aninvagination of the posterior end of the body, or a dilatationof the terminal part of the excretory duct, or both combined.A similar condition has not been observed in the other speciesof the genus, and as it is only visible on section Braun wasnot able to observe it. Ifc was present in each of my speci-mens. Its significance is not apparent.

A narrow tube with muscular walls leads from the apertureto the vesicle. Several muscle-fibres are grouped round theaperture in the form of a sphincter. The vesicle itself is ofsimple structure. It is lined throughout by a thin, delicatemembrane, in which small scattered epithelial cells can beobserved. The Avail is extremely irregular, being thrown intoinnumerable little wrinkles and folds. There is a depositionof muscle-fibres, both annular and longitudinal, but they arevery fine. The vesicle lies in a mass of very loose connectivetissue, and it extends as far forward as the posterior borderof the ovary, passing dorsally to the testes, by which it is com-pressed, but expanding in the spaces between the testes andovary. The anterior end is flattened and broadened and intoit the two lateral tubules enter. These pass forwards and aredistributed in the manner which Looss has fully described inBr. palliatum.1

The genital aperture is median, close in front of the ventralsucker. It is a narrow transverse slit with sphincter andradiating muscle-fibres. The genital sinus is of small size.The male duct opens into it on the right, the female on theleft. The radial fibres of the genital aperture pass into the

1 Op. cit., p. 405

STUDIES ON THI1 D1GENBTIO TRKMATODES. 433

longitudinal fibres of the cirrus-pouch and vagina. Thecirrus-pouch (fig. 7) is a pear-shaped or ovoid structureextending backwards nearly as far as the posterior border ofthe ventral sucker. I t thus reaches further back than in anyother species of the genus. At its posterior end it approachesthe dorsal surface of the body, and is separated from theventral sucker by the uterus. I ts maximum diameter is '3mm. The longitudinal mnscle-fibres of its wall have adiameter of "002—'004 mm., and are separated by spaces of•OO1-'OO4 mm. The annular fibres are much finer, •0004--002mm., with intervening spaces of •0007-<0015 mm. Thevesicula seminalis is of large size and occupies the greaterpart of the cirrus-pouch. I ts length is about "8 mm., butit displays numerous dilatations and convolutions. I tsdiameter vai'ies from '16 mm. to "28 mm. At its anterior endits wall is slightly invaginated into the pars prostatica, whichis a short S-shaped tube with a diameter of '066 mm. Theprostatic cells are comparatively few and are entirely confinedto the space around the pars prostatica. The cells are ova),with a long diameter of 012 mm. and nuclei of •0035--004mm. diameter. Amongst the prostatic cells there are a fewlarger cells measuring "019 mm., which do not staiu so deeplyand have faintly-staining, round nuclei measuring -0062 mm.At its anterior end the pars prostatica passes into a widelydilated ductus ejaculatorius, which presents a rather unusualcondition. In its retracted state, instead of being convolutedor wound upon itself, as is the case in many species, it iscrumpled up (concertina-fashion). In sections it presents agrating-like appearance (fig. 7), the lumen being alternatelycontracted and expanded. The crumpling, however, is notby any means irregular, fairly equal spaces being maintainedbetween the folds.1 The structure of the wall of the ductusdoes not differ from that commonly met with, there being an

1 A somewhat similar condition appears to exist in Distoninnialacre Lss., according to Looss's short description of that species(' Centralbl. f. Bakter.,' Abth. 1, vol. xxix, p. 40]). In the generaFellodistomuni and Steringophorxis an analogous condition exists,but in these the ductus is very short.

434 WILLIAM NICOLL.

inner layer of well-marked annular muscle-fibres and anouter layer of less distinct longitudinal fibres. The lumen islined by a rather thick cuticularised epithelium. In addition,however, to the two intrinsic muscle layers there are numerousother stout muscle-fibres passing from the ductus to the wallof the cirrus-pouch. These run more or less obliquely, buton eversion of the ductus they are drawn nearly parallel toit. To explain this peculiar condition of the ductus it seemsnecessary to consider that these extrinsic muscle-fibres exertthe most important action in retracting the ductus from itseverted position and that on account of their direction theycause it to fold up instead of winding on itself. What actionthe intrinsic longitudinal fibres take or why the eventualresult should be so different from that most frequentlyobserved are questions not easy to determine. No mentionis made of such a condition by Looss in the case Br.palliatum. His figure (PI. XXIII, fig. 8) represents theductus as a slightly tortuous tube of uniform calibre, widen-ing somewhat suddenly as it passes backwards and surroundedby a closely packed mass of gland-cells (Anhangsdriisen).The condition is therefore totally different from that inBr. oblongum, and it is a curious fact that two so closelyrelated species should present such an important feature ofdifference. Cells which stain deeply (gland-cells or myoblasts)are certainly present around the ductus, but they are com-paratively few in number and scattered in the midst oflooser tissue.

That the terminal part of the ductus functions as anexsertile cirrus there can be no doubt, for in one of myspecimens I found it extended about "06 mm. beyond thegenital aperture (i. e. about "2 mm. from the male aperture).In that case the anterior folds of the ductus were straightenedout, but the posterior folds remained, so that while the anteriorpart became a tube of uniform calibre, the posterior partremained in the condition above described.

The histological structure of the pars prostatica and vesi-cula seminalis does not differ from that in Br. palliatum.

STUDIES ON THE DIGBNETIC TEBMATODES. 435

The lining epithelium appears to be of somewhat lower type,and the muscle-layers are rather finer.

From the posterior end of the vesicula serninalis a singlevas deferens, "023 mm. in diameter, passes backwards to thelevel of the middle of the ovary, where it divides into tliepaired vasa. These remain close together for a short distanceand then separate to enclose the ootype. They join thetestes on their dorsal surface.

The testes are median, close together, and directly behindeach other. They occupy almost completely the middle thirdof the body, the posterior testis being exactly one third fromthe posterior end of the body, and the anterior testis a slightlygreater distance from the anterior end. Each has a ratherpeculiar shape, differing from that of the other. The anteriortestis is twice as broad as it is long, and its thickness equalsits length. It is therefore much compressed in the long axisof the body; not only so, but there is a distinct hollowingout both on the anterior and posterior surfaces, which isobvious only on longitudinal section. It consists of fourlobes, two large latei'al with small anterior and posteriorlobes. The posterior testis is much more symmetrical, beingcomposed of four nearly equal lobes—an anterior, a posterior,and two lateral. The anterior lobe is slightly indented onits ventral aspect, and the posterior shows one or twoirregularities, but the lateral lobes are almost uniformlyrounded. The lobing is quite deep, and the central part ofthe testis is about equal in size to each of the lobes. Thistestis is almost iso-diametric, and its maximum thickness isabout half its diameter. The thickness diminishes from thecentre to the periphery. This symmetrical shape might beregarded as the normal condition of the testes, and the shapeof the anterior testis as the result of deformity. In Braun'sfigure (fig. 3) the testes are shown as irregularly four-lobedbodies. The particularly long posterior lobe of the hindertestis, to which Braun draws attention, is evidently not aconstant feature. In Br. pall iatum the testes are lobed,but the lobes are smaller, more numerous, and do not appear

436 WILLIAM NJCOLL.

to have any constant direction. In Br . d e l p h i n i and B r .r o c h e b r u n i they are regularly ovoid. In a specimen of5*5 mm. length the sizes of the testes a re : Anterior, length•54 min., breadth l-20 mm., thickness *55 mm.; posterior,length "93 mm., breadth l-02 mm., thickness "52 mm. Thusthe diameter of the posterior testis is two elevenths of thebody length.

The ovary is median or very slightly to the right side,directly in front of the anterior testis and close to the ventralsurface of the body. It is separated from the ventral suckerby a very short space. Brann is not quite correct in sayingthat the ovary is globular in shape, for I find it constantlyslightly elongated transversely. The mean of three measure-ments gives the length "30 mm., breadth -37 mm., thickness•28 mm. The ovarian ova are largest towards the anterior-dorsal surface, and measure "0155 x •0087 mm. They arefusiform in shape, with large, round nuclei, measuring"0077 mm. Looss has figured and described the correspond-ing cells of B r . p a l l i a t u m , and it is evident that ourobservations agree fairly closely, except that I find the cellsconstantly rather more elongated. It is true,however, as Loossremarks, that these cells undergo various changes in shape.

The shell-gland complex (fig. 6) in this species differs inmore than one respect from that of Br . p a l l i a t u m , asdescribed by Looss, and particularly in the greatly reducedsize of the receptaculum seminis and the presence of a distinctyolk-reservoir. The oviduct (diameter "029 mm.) arises fromthe dorsal surface of the ovary. Not far from its origin itdescribes a complete circle upon itself- and then passes on ina straight course. About midway between the ovary and thedorsal sui-face of the body it dilates slightly and then turnsat right angles towards the left. At this point there isa small sacculation, on the l'ight side, no wider than the ovi-duct itself, and not differentiated from it by any markedconstriction. This is all that remains of the receptaculumseminis, and in all probability it no longer functions as such,for it never contains sperms and its lumen is almost entirely

STUDIES ON THE D1GENETIO TEBMATODES. 437

filled up with the hair-like processes of the epithelial cells.Moreover, its function seems to have been undertaken by theinitial part of the uterus, which in every specimen is packedfull of sperms (receptaculum seminis uterinum). Almostimmediately beyond the above-described turning of the ovi-duct Laurer's canal arises. It has a peculiar and almostconstant course. It passes nrst towards the dorsal surface,bending slightly to the left, but after traversing half thedistance it turns suddenly at right angles and runs posteriorlyparallel to the dorsal surface for a considerable distance,describing at the same time almost a complete semi-circlewith its convexity towards the right. It then again turnsabruptly at a right angle and passes in a more or less directcourse towards the dorsal surface, where it opens almost inthe middle line on the level of the anterior border of theanterior testis or a little further forwards. Its diameter isabout "023 mm.

From the origin of Laurer's canal the oviduct proceedson its way towards the ootype, running almost parallel to thesurface of the ovary. Just before entering the ootype itreceives the common yolk-duct, which passes forwards in arather sinuous course from a small reservoir lying a little infront of the anterior testis and almost midway between theovary and the dorsal surface. The ootype, which is situateddorsal to the left end of the ovary, bends forwards anddorsally to pass into the uterus. The ootype is wider(diameter "033 mm.) than the oviduct and the uterus is stillwider. The shell-gland is of large size. It does not investthe ootype closely, but its cells are diffusely scattered in thesurrounding,parts and communicate with the ootype by meansof long ducts. They are most numerous around the oviductand common yolk-duct. The histological structure of theshell-gland complex conforms to the usual type. The wholecourse of the oviduct is lined by a thick ciliated epithelium.The cilia are fairly long and are directed away from theovary. The receptaculum seminis is also lined by this ciliatedepithelium, the cilia of which are so numerous that they

438 WILLIAM NICOLL.

almost obliterate the cavity of the receptaculum. At irregularintervals in the epithelium of the oviduct there are singlelai'ge cells, evidently the same as those observed by Looss inBr. p a l l i a t u m . 1 For a very short distance Laurer's canalis also lined by ciliated epithelium, the cilia of which aredirected towards the ovary, i . e . in a direction opposite tothat of the cilia in the oviduct. I t is evident that thisarrangement has some relation to the prevention of theescape of ova or sperms through Laurer's canal. An analo-gous condition has been observed by Looss in Dis tomuuiu n i c u m Lss.3 The remainder of Laurer's canal is lined bya cuticularised epithelium. The ootype is lined by a regularnon-ciliated epithelium. The cells of the shell-gland do nothave the dense arrangement represented by Looss in Br.p a l l i a t u m . 3 They are fairly large cells, measuring -020 by•012 mm., and nuclei "005 mm.

The yolk-glands are richly developed, extending from thulevel of the phai-ynx to the posterior end of the body. Theyare mainly lateral, but their situation is not so much marginalas ventral and dorsal to the intestinal diverticula. Behindthe testis they unite in the middle line, also to a slightextent in front of the genital aperture. The follicles are notvery large, about "07—-08 mm. diameter. The componentcells are not well differentiated, owing to their containing alarge number of bright yellow refracting granules, which areabout '003 mm. in size. These granules are very difficult tostain, remaining untouched long after the other tissues aredeeply stained, but eventually they do take on the stain. Ifound that they did so more readily with saffranin andtoluidine-blue than with hsemalum and eosin. The small("004 mm.) round nuclei of these cells stain readily enough.I was quite unable to determine any differentiation betweencentral cell and peripheral cells as in S t e p h a n o p h i a l a

1 Op. cit., pi. xxiii, fig. 10.3 "Recherches sur la fanne parasitaire de l'Egypte"; in 'Mem.

Inst. Egypt,' iii (1896), p. 49.3 ' Zeitscli. f. wissen Zool.,' xli, pi. xxiii, fig. 13.

STUDIES ON THE DIGENETIO TREMATODES. 439

laureata. The transverse ducts run along the anteriorborder of the anterior testis to unite in the small medianreservoir. This contains a small number of yolk-cells inwhich the nuclei are still present. The common yolk-ductpasses forward to join the oviduct as already described.

It appears to be quite erroneous to speak of the secretionof the yolk-glands, as so many observers have done, for as Ihave shown both in the case of Stephanophiala laureataand the pi'esent species, the yolk substance is the result, notof a process of secretion, but of a process of proliferation offormative cells in a manner somewhat analogous to theproductiou of ovarian ova or spermatozoa. The yolk-glandsmust therefore not be regarded in the same category as theshell-gland and prostate-gland, which produce a true secre-tion. They are glands only in the same sense as the ovaryand testes are glands.

As in Br. palliatum, the uterus is confined to a verylimited space between the ovary and the level of the genitalaperture and between the intestinal diverticula on eitherside. It thus lies dorsal to-the ventral sucker and occupiesthe entire thickness of the body. Its course is impossible todetermine, owing to the greatly convoluted condition. Theinitial part, from the ootype, is lined with a highly ciliatedmembrane, but the cilia disappear after a short distance. Theuterus then becomes distended with ova, which are surroundedby a countless number of .sperms. This condition persistsfor about a third of the total length of the uterus, and it isevident that we have here to deal with a true receptaculumseminis uterinum, which is met with in several other speciesand which performs the function of the vestigial receptaculumseminis proper. The condition here is evidently muchremoved from that in Br. palliatum, in which, according toLooss, the receptaculum semiuis is full of sperms, andperforming its true function, while no mention is made of areceptaculum seminis uterinum.

The uterus terminates near the dorsal surface of the body,and the vagina passes almost in a straight line, dorso-

VOL. 5 3 , PAET 3 . NEW SERIES. 31

440 WILLIAM NICOLL.

ventrally, towards the genital sinus. It has a length of '45mm., and a diameter of "04-"09 mm., becoming narrow as itapproaches the genital sinus. Its section is not circular, buttriangular, and this is constant in every case, being appa-rently in correlation with the triangular shape of the ova. Itswall is thick ("012 mm.) and muscular, comprising the usualtwo layers, and it is lined by a thick cuticular membrane.

The ova are fairly numerous and measure '084 by *0436ram. The shell is light yellow and about *0035 mm. thick.The shape is characteristic. In longitudinal section they aresomewhat oval, but truncate at the anterior end and witha pointed knob, due to a thickening of the shell, at theposterior end. The operculum is very flat. In transversesection, however, they are triangular, the triangle beingequilateral. This peculiar shape of the ova was first noted,I believe, by Odhner1 in the case of Orthosplanchnusarcticus Odh., O. fraterculus Odh., Lecithodesinusgoliath (v. Ben.), and Brachycladium oblongum (Brn.).In his diagnosis3 of the sub-family BEACHYCLADiiNiE Odh. heregards it as a distinctive feature differentiating the sub-family, amongst other things, from the FASCIOLIN.*::. Hethus considers it to be of universal occurrence in the sub-family, and in particular in the genus Brachycladium Lss.He refers 3 to Poirier's * figures of the ova of Br. rochebruniand Br. delphini as indicating that the ova of the speciesprobably display the same shape. I fail to see any evidenceof this in Poirier's figures, and he himself certainly makes noreference to the triangular shape of the ova in transversesection.6 Odhner conveniently ignores Looss's statement6 that

1 " Die Trematoden des Arktischen G-ebietes " in ' Fauna Arctica,' iv,p. 343.

2 Ibid., p. 347. 3 Ibid., p. 346.4 "Trematodes noiiveaux on peu connus," in 'Bull. Soc. Philoniatiqxie,

Paris,' ser. 7, vol. x, pi. iv, figs. 3 and 5.5 It is quite possible that Odhner only means to imply that the ova

in Poirier's two species resemble those of the other BRACHYCLADIIN.*:in being thick shelled, -with flat operctiluni and pointed posterior end,but his statement in the sub-family diagnosis renders this doubtful.

c ' Zeitsch. f. Wissen. Zool.,' xli, p. 419.

STUDIES ON THE DK4ENJGTIO TJJEMATODES. 441

the ova in Br. pall iatum " haben fast die G-estalt einesRofcationsellipsoides." His hypothesis, therefore, althoughhighly probable, requires confirmation, and Looss's observationmust first be proved erroneous.

From the foregoing description it will be apparent thatBrachycladium oblongum (Brn.) and Br. palliatum(Lss.) cannot be confused, for the two species differ not onlyin their coarser anatomy, as Braun has already demonstrated,but also in many of. the finer details. It will also be admittedthat Br. oblongum does not conform strictly to the type ofBr. palliatum, but differs from it in such important featuresas the structure of the ductus ejaculatorius, the reducedcondition of the receptaculum seminis, with the presence ofa receptaculum seminis uterinum, and possibly most importantof all, the shape of the ova. How far any or all of thesedivergences are due to au error of observation on Looss's part,particularly as regards the ova, it- is impossible to say, butassuming them to be correct there can be little doubt thatthe two species cannot be included in the same genus. Notonly so but the condition of the ova would render Br.palliatum Lss. an atypical member of the BEACHYCLADIINAaccording to Odhner's diagnosis. On the other hand, Br.oblongum conforms to the sub-family definition, but is anaberrant member of the genus Brachycladium Lss. (typeBr. palliatum Lss.). At present it seems best to awaitfuller knowledge of Poirier's species before pronouncing-judgment on the matter.

Sub-family ALLOCREADIIM-; (LSS. 1899).

Genus Lebouria n. g.

Lebouria idonea n. sp., PI. 9, figs. 9-12.

This form occurred very regularly and always in largenumbers throughout the intestine of Anarrhichas lupus.Ib also occurred less frequently in the stomach. It is easily

442 WILLIAM NICOLL.

seen in the midst of the intestinal contents on account of itsdistinctly yellow colour.

It is of medium size, 1*5—2-5 mm. long, with a maximumbreadth of *7—l'O mm. Thickness "2 mm, fairly unifox'in exceptat the ventral sucker, where it reaches "3 mm. Its breadthis therefore nearly half its length, so that it is broader thanmost other ALLOCREADIINJ?. The shape is oval, slightlyattenuated anteriorly, considerably flattened dorso-ventrally.One example showed a curious deformity. In the posteriorhalf of the body on the level of the testis there was a largeindentation on the right side, an appeai-ance as if a part hadbeen bitten out. The specimen was uninjured, and althoughit was alive and moving actively the deformity still remained.It may be regarded as a pathological curiosity.

The smallest mature specimen obtained measured 158 mm.The largest immature specimen had the same length, andmany were found without ova just about this size or a triflesmaller, so that this probably i*epresents the size at which ovabegin -to appear, and may be taken as the minimum length ofadult specimens. The smallest immature example measured1-23 mm.

The cuticle is about "004 mm. thick and entirely withoutspines. True unicellular cutaneous glands, of the same kindas already described in Stephanophiala laureata, arepresent in the anterior part of the body, chiefly laterally.They are large, oval cells with distinct nuclei, and with theirlong axis in the length of the body, but they differ inappearance from the corresponding cells in St. laureata.They present a very distinct outline with pale, scanty, granularcontents. This may be due to a difference in the conditionof the cells or possibly to a slight difference in staining.

The subcutaneous muscular system is as usual. Thecircular fibres measure "0005 mm. and are sepai-ated byspaces of "004 mm. The longitudinal fibres measure "0007and are separated by "0135 mm. The diagonal fibres measure•001 mm. with spaces of '045-055 mm. The musclesthroughout the rest of the body are well developed, especially

STUDIES ON THE D1GKN15TIC TRBJJATODJSS. 443

in the neighbourhood of the ventral sucker. The myoblastsof the subcutaneous muscles are numerous, and arranged ingroups. Their nuclei measure "004— 005 mm.

The oral sucker is subterminal and nearly round, measuring•17—"28 mm. The ventral sucker is situated very nearly inthe middle of the body and is transversely oval. Its longaxis measures "41—"58 mm., its short axis "31—"48 mm. It isthus about twice the size of the oral sucker, and the trans-verse diameters of the suckers are respectively about onetenth and two ninths of the body-length. Tlie internalstructure of the suckers offers nothing peculiar.

The pre-pharynx is distinct and rather wide. Thephai-ynxis of comparatively large size, measuring *15—"21 mm. indiameter. It is neai'ly globular, but the breadth is slightlygreater than the length. It is proportionately much largei*than it is in any other member of the ALLOCREADIIN.E. Theoesophagus is about as long as, or a little shorter or longerthan, the pharynx ("l-'lS mm.). In section it is transverselyoval. The intestinal bifurcation occurs almost midwaybetween the suckers. The diverticula are fairly wide ('04—"07 mm. in a large specimen). They pass round the sides ofthe ventral sucker and, taking up a dorsal position, extendnearly to the posterior end of the body. The oesophagus issharply differentiated from the diverticula, not only by thechange in the nature of the lining, but also by a well-marked constriction (fig. 10). The bifurcation is of thenature of a dilated sac formed by the fusion of the initialparts of the diverticula. In appearance it rather simulatesa small ventricle. The pharynx and oesophagns are linedwith a cuticular membrane; that of the former is probablytrue cuticle, that of the latter is transformed epithelium. Inany case the two are not identical, for the pharyngeal liningis thicker and stains more deeply than the oesophageal. Thebifurcation and diverticula are lined throughout by a well-developed epithelium, the nuclei of which are round andmeasure '0052 mm. Numerous hair-like processes are givenoff from the cells. The musculature of the alimentary canal

444 WILLIAM NICOLL.

is well developed. The fibres of the oesophagus are stouterand more closely set than those of the diverticula. Theyhave a diameter of about "0015 mm., and are separated byabout the same distance or slightly more in the case of thelongitudinal fibres. Those of the diverticula measure•0004 mm. with spaces of "0035 mm. in the case of the annularfibres, and "0075 mm. in the case of the longitudinal fibres.These figures of course are only approximate, for there isgreat variation with the state of contraction. A moderatenumber of circum-cesophageal cells (myoblasts) are present.

The excretory system is of simple type. There is a smallundivided vesicle not extending further forward than theanterior testis and opening by a pore at the posterior end ofthe body. From the vesicle two narrow, transversely oval,collecting tubes are given off. They pass outwards to lie closeto the outer side of the intestinal diverticula. Their coursethereafter was not followed.

The testes are two transversely-oval bodies of ratherirregular outline lying midway between the ventral suckerand the posterior end of the body. They are very closetogether, practically contiguous, and very often somewhatobliquely set, one behind the other. The anterior testis isdisplaced to the left side, while the posterior is nearly medianor a little to the right. In many specimens they were founddirectly tandem, but no other difference could be found inthose specimens, so they are probably only a variety. Thetestes are very nearly equal in size, the posterior being, ifanything, a little larger. The long diameter measures•31—"37 mm., the short diameter "19—"22 mm. The vasadeferentia arise from their anterior surface and pass forwardsventral to the shell-gland complex as two almost straightlines towards the vesicula seminalis.

The cirrus-pouch (fig. 11) is of no great size, but it appearsshorter than it actually is, owing to the backward displace-ment of the ventral sucker. It extends only a short distancebeyond the anterior border of the sucker. Its total length isabout *4 mm. The narrow anterior part, which has a terminal

STUDIES ON THE DIGENETIO TEBMATODES. 445

diameter of about "03 mm., usually runs straight back fromthe genital aperture, while the thicker part is bent on thiseither to the right or left. The diameter of the latter reachesa maximum of "09 mm. Its wall consists of the usual doublelayer of muscle-fibres, which have a diameter of about #0009mm. and are closely set. The vesicula seminalis is ve-markable for the extent to which it is convoluted (fig. 11),exceeding that of Podocotyle atomon (Rud.) in thisrespect. It appears, however, to have a fairly definiteconfiguration. From the end of the cirrus-pouch it passesforwards in a curve towards the right. It then turnscompletely on itself and bends back in an S-shaped coursenearly to the posterior end of the pouch, where it againturns and runs forward almost parallel to the first part. Itthen passes into the ductus ejaculatorius, which almostimmediately bends backward, describes a turn, passesforwards again, only to describe another complete turn, afterwhich it runs forwards in a sinuous manner, but withoutfurther convolutions. The diameter of the vesicula seminalisis '04, mm.; that of the ductus is about '015 mm.

As in Podocotyle atomon (Rud.) no well-differentiatedpars prostatica occurs on the ductus. Around the initial partof the ductus, however, there is a considerable number oflarge cells which occupy the usual position ot' the prostaticcells. They differ from the corresponding cells in Stephano-phiala laureata , Brachycladium oblongum and otherspecies which I have examined. The cell body appears to bevery tenuous and almost invisible, but the nucleus andnucleolus stain very brightly. The nucleus is large andround, measuring "0068 mm., the nucleolus "0018 mm. Theycertainly do not lend the impression of being gland-cells, butfrom their position they can hardly be otherwise. They arequite distinct from the " Begleitzellen" or myoblasts whichare present in large numbers around the anterior two thirdsof the ductus. The latter are much smaller cells, stainingdeeply and resembling the peri-vaginal cells.

The genital aperture is situated midway between the

446 W1LUAM NICOLL.

suckers, just over the intestinal bifurcation. In most speci-mens it is approximately median, but in many it is displaced alittle to the left side, and in a few a little to the right. Thenormal position may therefore be regarded as median, butwith variations, and this probably indicates one of the initialstages of the transformation to a distinctly lateral positionas in Podocotyle . The only other members of the ALLO-CKEADiiNiE, as at present recognised, which have a lateralgenital aperture, are A. tumidulum (Rud.) and A. a n g u s -t icol le (Hausmann), in the former of which the aperture iswell to the left, in the latter only slightly. In. all the otherspecies it is median, and it is surprising that more forms havenot been described showing intermediate stages of this dis-placement, for it is evident that it can only have occurred by agradual series of changes. It would be interesting to dis-cover the reason of the transposition and why it is to the left.

A small genital sinus is present, into which the male ductopens on the right, the female on the left.

The ovary is situated immediately in front and to the rightside of the anterior testis, with which it is contiguous. Italso lies close beside the intestinal diverticulum, and isseparated from the ventral sucker by a distance equal to thediameter of the ovary. It is a round, almost globular body,with entire margin and measures #16-"17 mm. in diameter.The ovarian cells are largest anteriorly, beiog about "01 ram.in size. The oviduct arises from the anterior dorsal surfaceof the ovary, and passes in a curved course towards thereceptaculum seminis. This is a large oval sac, measuring•1-"16 mm., attached to the oviduct without the intervention ofa pedicle. Laurer's canal arises directly from the i-eceptaculumand runs almost straight in towards the middle line of thebody. The exact position of its opening could not beascertained. The receptaculum lies dorsal to the ovary, butits position is variable, being sometimes in front of the ovary,sometimes behind it. In fig. 12 it is shown in the latterposition. From the receptaculum the oviduct passes acrossthe ovary to the shell-gland, before entering which it is

STUDIES ON THE DIITENETIC TBEMATODBS. 447

joined by the common yolk-duct. The shell-gland lies closeto the left side of the ovary and receptaculum. It is a small,compact structure with cells measuring "015 mm. and nuclei•0058 mm. The cells have a distinct staining reaction, takingon a uniform dull red or reddish-purple with haenialum-eoain.

The small yolk-reservoir lies dorsally in the middle line ofthe body just in front of the anterior testis. The yolk-glandsare lateral, extending from the pharynx to the posterior endof the body, where they unite behind the testes. Anteriorlya few follicles find their way acx*oss the middle line under thedorsal surface, but none ventrally. Posteriorly the follicleslie under both the dorsal and ventral surfaces and surroundthe intestinal diverticula. They are of moderate size, compris-ing twelve to twenty cells, which measure about '023 mm. indiameter, and have large ("006 mm.), round, central nuclei.

The uterus is limited in extent, being confined betweenthe ovary and the posterior border of the ventral sucker, butalso filling up the space between the sucker and the leftintestinal diverticulum. The vagina is shorter than the cirrus-pouch, lying to the left of it and slightly dorsal. Its diameterdiminishes from "035 mm. to '023 mm. It has the usualmuscular structure with numerous accompanying myoblasts.

The ova are not numerous (about sixty). They are lightyellow, with a very thin shell. Their shape is broadly oval,but at the anopercular pole there is a small excrescence of theshell forming a small knob-like projection.1 This is of variablesize and is sometimes absent. It might be regarded as indicat-ing an initial stage towards the filamented condition of the ovain Helicometra. They measure '0715—'0746 mm. in lengthby -039--0435 mm. in breadth. Average '073 by "041 mm.

From Anarrhichas lupus six species of Distomids haveat one time or another been recorded. The first of these ;iretwo species mentioned by Rathke3 and named by Rudolphi3

Distomum incisum and D. anarrhichas lupi, found re-1 For directing iny attention to this I am obliged to Miss Lebour.2 ' Dansk. Selsk-Skrift,' v (1), (1799), p. 70, pi. 2, figs. 3, a, b.3 ' Bntoz. Hist. Nat.,' ii (1), (1809), pp. 361, 435.

448 WILLIAM NICOLL.

spectively in the intestine and the stomach. The description ofboth is extremely scanty and hardly admits of positive identi-fication. D. incisutn, it is true, was regarded as identicalwith D. fell is Olsson by Stossich, but this is denied byJacoby.1 It is almost certain that neither species is identicalwith Lebour ia idonea. Distomum atomum Rud. isnoted by vonLinstow2 under A n a r r h i c h a s lupus, but inthe reference3 it is only recorded from P l a t e s s a flesus.The peculiar condition of the ova which von Linstow describesdistinguishes his specimens from Podocoty le atomon(Rud.), and renders it not at all improbable that they werereally specimens of Lebour i a idonea. The first mention ofthis actual species is by Miss Lebour,4 who has kindly allowedme to describe it in consideration of a previous communicationof its discovery Avhich I had made. It is not the only specieswhich occurs frequently in the intestine of A n a r r h i c h a slupus, for in invariable association with it, but usually in thelower parts of the intestine, I have met the much smaller formZoogonus rube l lus (Olsson). This is the first record ofthe latter species from the cat-fish, and also the first timeit has been met with in British waters, yet it is a constancparasite of the cat-fish in this locality.

It remains to differentiate Lebour i a idonea from alreadyrecognised members of the sub-family ALLOCREADIIN^;. PromPodocoty le (Duj.) it is easily distinguished by the medianpositiou of the genital aperture; from Hel icorne t ra Odhnerby the non-filamented condition of the ova, and from Allo-c read ium Lss. sens, str., by the oblique position of the testes,the backward situation of the ventral sucker, and the absenceof distinct pars prostatica. Amongst the unclassified formsit appears to bear most resemblance to Dis tomum tumi-dulum Rud.,5 but that species is more elongated, has a

1 ' Arch, f. Naturg.,' lxvi, p. 13.2 ' Coinpend. d. Helminth. Nachtrag.,' p. S2.3 ' Arcli. f. Naturg.,' xlir, p. 225.4 ' Northumberland Sea Fisheries Report for 1907,' p. 16.0 Odhner, " Revision einiger Arten der Distonmmgatfrung Alloerea-

dium Lss.," in ' Zool. Jahrb. Syst.,' xiv, pp. 503-505.

STUDIES ON THE D]GENETIC TBEHATODES. 449

distinctly lateral genital aperture,1 smaller ova, and roundtestes. Were it not for the lateral genital aperture it mightl'eadily enough be included in the genus Lebouria, arid itis certainly more nearly related to this genus than it is toPodocotyle. This affinity may be indicated by re-naming thespecies (Lebouria) tumidula K,ud. From the other ALLO-CBEADIIN ;, Lebouria idonea is much more easily dis-tinguished.

In proposing this species as the type of a new genusI have been influenced by the fact that it is impossibleto include it under the genus Allocreadium Lss., andtherefore its description as an Allocreadiuni sp. wouldhave been erroneous. Moreover, it appears to be the repre-sentative of a group with features quite as well defined asthose of He li come tr a and Podocotyle, and further, it is notan isolated species, for in an American form described byLinton2 from Bairdiella chrysura we have what must beregarded as an additional number of the genus. Linton'swork is, unfortunately for our present purpose, more of abionomic than morphological character, so that his treatmentof the species is not so exact as we might have desired. Hisfigures, however, give a fairly good idea of the form, and itsclose resemblance to Lebouria idonea is not difficult tomake out. We note the expanded shape of the body, thebackward position of the ventral sucker with the intestinalbifurcation far in front of it, the oblique, or sometimesmedian, position of the testes, the round ovai-y, extensiveyolk-glands, limited uterus, short cirrus pouch, and mediangenital aperture. With regard to the position of the genitalaperture it is shown in fig. 168 midway between the ventralsucker and the intestinal bifurcation, but from the forwardposition of the ova it may possibly be found to be somewhat

1 I Lave since found in Labrus bergylta a Distornid which I aminclined to identify as Disttfinnm ttimidulnm, and in it the genitalaperatnve is median or very slightly displaced.

2 'Bull. Bureau TJ.S. Fisheries,' xxiv (1904), p. 389, pi. xxiii, figs. 168-170.

450 WILLIAM. NiCOLL.

nearer the bifurcation. Linton was somewhat doubtful of theidentity of this species and hesitated to assign to it a specificname. I therefore propose for it the name L e b o u r i ao b d u c t a n. sp., and add the following short descriptiou.

Length about *8 mm.; breadth half the length; oralsucker *12 mm.; ventral sucker oval, a little in front of themiddle of the body, diameter "17 mm. (this is probably theshort diameter, for in Linton's figures the transverse dia-meter is always at least twice that of the oral sucker).Pharynx, length '06 mm.; oesophagus short; genital aperturea little behind intestinal bifurcation. Testes much largerthan those of L e b o u r i a i d o n e a , irregularly shaped, in pos-terior third of body. Cirrus-pouch short, extending a littlebeyond the anterior border of the ventral sucker. Ovarytransversely oval, on a level with anterior testis or a little infront, on right side. Yolk-glands only reaching intestinalbifurcation, not uniting in front but filling up space behindtestes. Ova few (five to twenty) measuring "063 by '035 mm.

From a comparison of these two species the genusL o b o u r i a may be defined as follows :

Small ALT,OCREADIIN;E with broad, flat, oval body. Ventralsucker oval, larger than oral sucker, situated about themiddle of the body or a little in front of it. (Esophagusshort, intestinal bifurcation midway between suckers. Excre-tory vesicle simple, sliort. Genital aperture median orslightly displaced, near the intestinal bifurcation. Testes ofirregular shape, oblique or tandem, in the middle of thepost-acetabular region. Cirrus-pouch short, not reaching themiddle of the ventral sucker, containing a convolutedvcsicula seminalis and ductus ejaculatorius, but lacking awell-differentiated pars prostatica, although prostatic cellsare present. Ovary rounded, on the right side, on a levelwith anterior testis or immediately in front of it. Recep-taculum seminis and Laurer's canal present. Yolk-glandsextending in front of ventral sucker. Uterus short; ova few,thin-shelled, with small protuberance at the anopercular pole,measuring about "07 by "04 mm.

STUDIES ON THE DIGENET1C TRKMATODES. 451

Habitat.—Stomach and intestine of marine fishes.Type . — L e b o u r i a idonea n. sp.; including also L.

o b d u c t a n. sp.Mention may be made here of another species which, bears

some resemblance to L e b o u r i a idonea , namely, Dis to-mum a l a c r e Lss.1 from L a b r u s m a c u l a t u s and otherLabridae. At first sight only comparatively unimportantdifferences are apparent between the two, such as the slightlylateral position of the genital aperture, the somewhat elon-gated testes aud the rather larger ova. The structure of theterminal part of the male genital duct, however, is differentfrom that not only in L e b o u r i a but also in other AIXOCREA-DHN.S:, and for that reason, apparently, Looss has hesitatedin assigning to this species a systematic position.2

Genus P o d o c o t y l e (Duj.) Odhn., 1904.

= S i n i s t r o p o r u s Stafford, 1904.

Podoco ty l e a tomon (Eud.) PI. 10, fig 28.

= Dis tomum v i te l losum Linton. Johnstone,'KeportLancashire Sea Fisheries/ for 1906, xxi (1907), pp 182-185,fig. 15.

For the opportunity of examining these specimens 1 amindebted to my friend Mr. • Johnstone, who kindly put themat my disposal. Their resemblance to Distoinum vi te l -losum Linton is not borne out on close examination, andthey have proved to be in reality a species of P o d o c o t y l e ,most probably P . a t omon (R.). At first sight I wasinclined to regard them as distinct from the latter species.The unusually cylindrical shape of the body, the excessive

1 ' Centralbl. fur Bakter.,' 1st Abth., xxix, pp. 401-402, fig. 2.8 In a paper by Stossich (in ' Boll. Soc. Adriat.,' xxii, p. 211-217),

which has not yet found its way into the London libraries and wliich Ihave therefore not had an opportunity of seeing, Distomuin alacreLss. is included in the genus Allocreadium (not sens, strict). Ifthis species be really a menibei of the ALLOCKEADIINJ, it must occupya place very near the gemis Lebouria.

452 WILLIAM NICOLL.

prominence of the ventral sucker and the conspieuousness ofthe yolk-ducts were features unfamiliar to me in my previousexperience of the species. As a matter of fact, however,they are due to the method (in fresh water) which Johnstoneemployed in killing his specimens. I have since found Podo-cotyle a tomon in various species of fish, and tried the ex-periment of killing some in fresh water, in which they assumedthe same shape and appearance as Jolmstone's specimens.

One of the most striking features of Johnstone's specimenswas the distinctness not only of the yolk-ducts but also ofthe yolk-glands themselves. On that account their disposi-tion could be easily observed, and this is shown very well inJohnstone's figure. One point to which he makes no refe-rence is the occurrence, in about every third specimen, of anasymmetrical group of follicles in front of the ventral suckeron the right side. This had not the linear arrangement ofthe other follicles, but was more dendritic, and from it aseparate duct passed down to join the longitudinal duct.This asymmetrical group was never observed on the left side.I have since collected a number of specimens showiug thesame characteristic but differing in no other respect fromP o d o c o t y l e a t o m o u . I t seems to indicate what might beregarded as a distinct variety, and for this I propose theprovisional name P . a tomon var. d ispar .

During a recent visit to the Firth of Clyde, I have obtainedPodoco ty le a tomon from numerous species of fish, G-adusvi rens , Gr. pol lachius , P l eu ronec t e s flesus, PI.platessa, Cottus scorpius, C.bubalis and Centronotusgunnellus, and have been struck with the remarkabledivei'sity of form which it presents. It displays valuation inthe extent of the yolk-glands, the length of the cirrus-pouch,the shape and situation of the testes, and, in particular, thesize of the ova. I have to add Gastraea spinachia(fifteen-spined stickleback) as an additional host on the eastcoast, and in the specimens from this host the ova wereexceptionally large, reaching a length of nearly -1 mm. ThisTrematode, if all the specimens be really identical, is very

STUDIES ON THE DIGENETIO TREMATODES. 453

widely distributed, it having now been recorded fromthirteen different hosts in this country.

On t h e c l a s s i f i c a t i o n of t h e ALLOCREADiiNiE.

We are now in a position to recognise, at least, four well-defined groups of the ALLOCREADIIN2E, namely, the generaA l l o c r e a d i u m Lss., sens strict., H e l i c o m e t r a Odhn.,Podocotyle (Duj.) Odhn. and L e b o u r i a Mihi. The types ofother groups have been indicated by Odhner,1 and he hasalso constructed a key for the diagnosis of several species.2

In all probability the ultimate division of the sub-family willproceed along the lines he has laid down, with certainmodifications. The imperfect knowledge which we as yetpossess of the internal structure of many of these forms renderspremature any attempt at a complete classification of thesub-family, and we must be content for the present withspeculations. On the other hand, it is advisable in theinterests of systematic work, that as many forms as aresufficiently well known should be assigned their true genericplace, and on that account I venture to propose, as the typesof two new genera, two species which have already beenconsidered by Odhner as probable generic types, and ofwhich I have personal knowledge,3 namely, D i s t o m u ml a b r a c i s Dujardin and Dis t . g e n u Rud. Both specieshave been re-described by Odhner,* and the first also byJohnstone.6 I propose Dis t . l a b r a c i s Duj. as the type ofthe new genus C a i n o c r e a d i u m with the following pro-visional definition :

Large ALLOCREADiiNa; with extended, flattened body.1 " Die Trematoden des avktischen Gebietes "; in ' Fauna Arctica,'

iv, p. 327.2 " Revision einig. Arten der Gattung Allocreadiinae," in ' Zool.

Jalirb.,' syst. xiv, p. 516.3 Thanks in the first instance to my friend Mr. Johnstone, who sent

me his specimens of Allocreaditim labracis Duj.4 ' Zool. Jahrb.,' syst. xiv, pp. 496-499 and 514-515, pi. xxxiii, figs. 3

and 11.5 ' Trans. Biological Soc.,' Liverpool, xxii (1908), pp. 44-53, pi. iii.

454 WILLIAM NICOLL.

Ventral sucker near the middle of the body, globular orslightly oval and not projecting much. (Esophagus short,bifurcation far in front of ventral sucker. Excretory vesiclesimple, short. Genital aperture median, not far behind intes-tinal bifurcation. Cirrus-pouch long and slender, not extend-ing beyond ventral sucker. Vesicula seminalis convoluted,ductus ejaculatorius long; true pars prostatica absent,but prostatic cells present. Ovary on right side, imme-diately in front of testes, distinctly trilobate. Keceptaculumseminis large, giving off Laurer's canal directly. Yolk-glands extensive, filling up considerable part of neck. Yolk-follicles arranged peripherally. Ova without filaments, veryvariable in size, "07—"10 mm. by "04— "06 mm.

For .Dist. genu Rud. I propose the new generic namePeracreadium, with the following definition :

Small to medium sized ALLOCKEADIIN.®, with elongatedovate, slightly flattened body. Ventral sucker not veryprominent, situated about the end of the anterior third ofthe body. CEsophagus short, bifurcation midway betweensuckers. Excretory vesicle simple. Genital aperture median,at intestinal bifurcation. Cirrus-pouch very long and slender,extending as far back as the level of the ovaiy ( = about onethird of the body length). Vesicula seminalis convoluted;ductus ejaculatoi-ius long; d is t inc t pa r s p ros ta t i ca pre-sent . Ovary globular, with entire margin, situated a little tothe right side of the middle line, immediately in front of thetestes or separated from them by a small part of the uterus.Testes usually transversely oval, with entire margin, situatedabout the middle of the post-acetabnlar region. Yolk-glandsextensive, occupying considerable part of neck and filling upposterior part of body. Ova without filaments, very variablein size, "07—'10 mm. by "03—'06 mm.

Habitat.—LABHIDJE, SO far as known.Type.—Peracreadium genu (Rud.). Also P. com-

mune (Olss).Between these two new genera the main differences consist

in (1) the position of the ventral sucker; (2) the shape of

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456 WILLIAM NICOLL.

the ovary and possibly also of the testes; (3) the length ofthe cirrus-pouch; and (4) the presence of distinct parspi-ostatica.

Of the remaining unclassified forms neai-ly related to theAILOCREADIINJ? I shall refer here only to those described byStossich1 and Linton.2 Of these D i s t o m u m unabrineeStossich, as already indicated by Odhner, probably representsa distinct genus type., the characteristics of which are: (1) therather stout, broad body; (2) the very short (or absent)oesophagus; (3) the long cirrus-pouch reaching the ovary;(4) small round testes; (5) globular ovary (on left ?) ; (6)median genital apertui-e; (7) yolk-glands confined behindventral sucker. These form a group of features sufficientlyimportant to exclude the species from any of the alreadyformed genera. D i s t o m u m o b o v a t u m Molin and D.m or m y r i Stoss. bear much resemblance to each other and toD . umbr inse Stoss. They differ from the latter, however,in the flatter body, the apparently lateral position of thegeuital aperture, the yolk-glands extending into the neck,the ovary on the right side and the transverse oval shape ofthe testes. These three species are probably more nearlyi-elated to P e r a c r e a d i u m than to any other genus. Anotherspecies which appears to approach those in some degree isthat depicted by Linton in fig. 165 and found in S p h e n o i d e sm a c u l a t u s . I t is characterised by a very small ventralsucker, a cirrus-pouch just extending beyond the sucker,transverse testes and yolk-glands confined behind ventralsucker. D i s t o m u m scorpsenae Rud. Stoss. (I, p. 158,fig. 20) is an extremely doubtful member of the sub-family.I t is characterised by the peculiar shape of the body3 and of:the oesophagus. Otherwise it bears a distinct resemblance toP o d o c o t y l e , but the ovary is globular and the cii'rus-pouchmay prove to be of unique structure. D i s t . f a s c i a t u m Rud.

1 "Brani Elinint. Tergest.," in 'Boll. Soc. Adriat.,' ix, No. 1 (1885),pp. 158-161, pi. iv-vi; and No. 2 (1886), pp. 44-49, pi. viii.

- " Parasites of Fishes of Beaufort, North Carolina," in ' Bull. Bur.Fisheries, U.S.A.,1 xxiv (1904), pp. 321-428, pi. xxii-xxiv, xxviii.

3 This peculiar shape can, however, often he ohserved in Podoco-tyle atomon.

STCJD1KS ON THE DIGBNETIO TREMA.TODBS. 457

Stoss (I, p. 160, fig. 25) is regarded by Odhner1 as wronglyidentified. The long cirrus-pouch brings this species intorelation with Peracreadiuin. In other respects it alsoagrees closely with this genus.2

Distomum vitellosum Linton (p. 335, figs. 176—178) is aspecies which shows some affinity to the ALLOCRBAWiNa:, butis distinguished by the peculiar structure of the ventralsucker. Liaton has described this species from numerousfish, but his descriptions are so conflicting that it is either avery variable species or it is a combination of two or moredistinct species. It is undoubtedly a genus type, but itsstructure is not sufficiently well known for it to be definitelyincluded amongst the ALLOCBEADIIN ;.

One other species may here be mentioned, namely, Dis-tomum globiporum Rud. Linton (p. 334, figs. 159, 173,198) from Leiostomus xanthurus and other fish. Thisspecies is quite incorrectly identified. It belongs to the sub-family LEPOCESADIINJJ: Odhn., but to which genus it is diffi-cult to say. It seems, however, more nearly related toLepocreadium than to Lepodora (Lepidapedon), andit is not identical with any of the European forms. Thespecimens which Linton obtained certainly do not all belong tothe same species. Those from Fundulus majalis (p. 356,fig. 159) are small with equal suckers, round testes, andapparently without spines, and with the genital apertureimmediately in front of ventral sucker. Those from Ortho-prist is chrysopterus (p. 378) are twice as large, withsmaller ova, ventral sucker half as large again as oralsucker. Genital aperture immediately behind pharynx, andvitellaria extending, forward to the middle of the neck.Those froni Leiostomus xanthurus (pp. 393—394,figs. 173,198) are a mixed lot, some with spines, others without. The

1 " Revision der Gattung Allocreadinm," in ' Zool. Jahrb.,' syst. xiv,p. 486.

: In Stossicli's latest paper (see p. 61, note 2) on these species, Allo-cretidium eharacis Stoss., A. mormyri, and A. umbrinse are dealtwith. A new species, A. dnbium, is added. Whether he deals withDistomum faseiatum Bud. or not I am unaware.

458 WILLIAM NICOLL.

ventral sucker is distinctly larger than the oral sucker, thegenital aperture is immediately in front of the ventral sucker,testes lobed, and ova nieasm-e about "10 by •05-"06 mm.The specimens which Linton found on August 10th, 17th and30th (pp. 393-394, figs. 198-199) appear to represent a fairlydistinct species, the characters of which may be summed upas follows: Length 3 mm.; breadth 1*25 mm. Oral sucker•4 mm. in diameter; ventral sucker -5 mm. Cuticle coveredwith scale-like spines on dorsal surface and anterior ventralsurface. Pharynx "12 mm. Pre-pharynx and oesophaguseach about same length as phai'ynx. Genital aperture median,immediately in front of ventral sucker. Cirrus-pouch extend-ing back to anterior border of first testis. Testes median,tandem, slightly lobed, situated near the middle of the post-anetabular region. Ovary sub-globular not far behindventral sucker, separated from testes by the end of the cirrus-pouch, median or slightly to right side. Yolk-glands lateralto outer side of intestinal diverticula, filling space behindtestes, not extending in front of ventral sucker. Ova notnumerous, measuring '10—"12 by "05—"06 mm. To this speciesthe provisional name (Lepocreadium) serospinosum sp.inquir (= Distomurn globiporum Rud. Linton, 1904, e.p.)may be given.

Sub-family FELLODISTOMINA;, n. sub-fam.

Genus Fellodistomum (Stafford 1904).Fellodistomum f ellis (Olsson, 1868). Pi. 9, figs. 13, 14.

Distoma f ellis Olsson, "Entozoa, iakt. Skand. hafsfisk.,"in 'Lunds Univ. Arssk.,' iv (8), pp. 44-46, pi. v., fig. 94,A, B.

Distomum fellis Olsson, Stossich, "I. Distomi dei Pesci,"in 'Progr. d. Ginnasio comm. super. Trieste.,' 1886, p.24.

Distouiuui fellis Olsson, Jacoby, "Beitr. v,. Kenntnis. einig.Distomen," in ' Arch. f. Naturg.,' lxvi (1) (1900), pp.12-16, pi. ii, figs. 8-12.

STUDIES ON THE DIGENETIO TREilATODES. 459

? Fellodistomum iucisum (Rud.) Stafford, " Trematodes.from Canadian Fishes," in 'Zool. Anzeig.,' xxvii (1904),p. 486.

This species has already been recorded from the east coastof Britain by Miss Lebour. It is a remarkably frequentparasite of the cat-fish (Anarrhiclias lupus) being metwith in almost every specimen, young and old. Its habitatis exclusively the gall-bladder. Fifty examples, at least, canusually be obtained from one host.

On the question of the identity of this species with twospecies found by Rathke1 in Anarrhiclias lupus and namedby Rudolphi,2 several authors have ventured an opinion.Van Benedin3 considered D. fellis Olss. synonymous withD. incisum Rud. Stossich also evidently considered thetwo species identical, but retained Olsson's name. Jacobyrepudiated the possibility of such identity. Stafford, leavinghis reasons unexplained, adopts Rudolphi's name, and makesDist. incisum Rud. the type of his genusFellodistomum.How he identifies the species which he describes withRudolphi's species is to me not very apparent. It has littlein common with Rudolphi's description.

As regards D. incisum Rud. my opinion coincides withthat of Jacoby. By no legitimate means can the formfigured by Rathke and described by Rudolphi be made toagree with D. fellis Olsson. On the other hand, Rathke'ssecond species, which Rudolphi4 provisionally named Dist.anarrhichee lupi, bears an undeniable resemblance toDist. fellis.5 The only description of this form, beyond itshabitat and size, is contained in Rathke's words "corporeelongato cameo, apertura dorsali rotunda annulo luteo

1 ' Dansk. Naturhist-Selsk. Skrivt.,' v (1799), p. 70, pi. ii, fig. 3.•> ' Bntoz. Hist.,' ii (1), p. 361.3 ' Mem. Acad. Roy. Belg.,' xxxviii (1870), p. 48.4 ' Entoz. Hist.,' ii (1), p. 435.5 Olsson undoubtedly recognised this, for he marks D. anurrhichas

lupi as doubtfully identical with D. fellis. At the same time hecompletely ignores such a possibility in the case of D. incisum Rud.

460 WILLIAM NICOLL.

cincta," but these words describe exactly the chief featureswhich struck me -when I removed my first specimens fromthe gall-bladder of their host. The thick, fleshy bodyextended vigorously towards both ends, the large knob-likeventral sucker (apertura dorsali), pale pink or flesh-like incolour and surrounded by a strikingly bright yellow ringcontrasting strongly with the dull greenish hue of the rest ofthe body. These appearances are lost on preservation, andit was on this account, I believe, that Jacoby, who examinedpreserved material, Avas not impressed with Kathke's descrip-tion. A most potent objection to the identification of Dis t .a n a r r h i c h s e with D. fell i s is the difference in habitat, forRathke's specimens occurred in the stomach. Various hypo-theses might be advanced to meet this difficulty, but it makesno difference to the matter in hand, for, as Looss hasexplained, such names as D. a n a r r h i c h s e l u p i were notintended by Rudolphi as specific names, so that the name D.fe l l i s Olsson remains good.

With regard to Stafford's specimens, the ovary is describedon the left side and the testes as large and spherical.According to Jacoby's observations, which I confirm, theovary always lies on the right side and the testes are obliquelyoval in D i s t o m u m fe l l i s . This renders it doubtful ifStafford's specimens are really identical with D. fe l l is , butit is possible that Stafford's statements may be due to a slipof the pen.

My adult specimens measure 2*5—3-3 mm. in length and1*1-1'6 mm. in breadth. The normal breadth seems thereforeto be about half the length, but the animal is capable ofconsiderable extension. In the contracted state the breadthmay almost equal the length and the animal becomes nearlyglobular. The shape in the quiescent state is most probablythat represented by Jacoby. The body is thick and nearlyopaque.

Numerous immature specimens were found, and thesemeasured 1*1—2-5 mm., so that in this species maturity isreached at a size of about 2"5 mm.

STUDIES ON Tflli DIGENET1C TBEMATODES. 461

As already mentioned the large ventral sucker surroundedby a yellow ring is the most prominent feature seen onventral view. On the dorsal aspect the two intestinaldiverticula show up very conspicuously by reason of theirdark green contents.

The oral sucker is sub-terminal and globular, measuring•40--45 m m . The ventral sucker is also globular, situated alittle behind the centre of the body. Its aperture may beeither circular, transverse or diamond-shaped. Its diameteris 9-1 0 mm., therefore about twice that of the oral sucker.Although of such great size, it is deeply sunk into the bodyand does not project much above the surface.

The histological structure of the suckers, especially theventral sucker, presents many features of interest, and heremy observations do not entirely agree with those of Jacoby.There are three chief varieties of cells: First, the largemyoblasts (fig. 14, G Z). These are extremely few, notmore than two or three appearing in any one section. Theyare very large cells, measuring '03—"05 mm., and, as Jacobyobserved, the cell-body stains homogeneously deep red. Thenucleus is central and,oval in shape, measuring about *02 by•015 mm. I t is traversed by a well-defined chromatin net-work, in the midst of which is situated a globular nucleolus,the diameter of which is 007 mm. This type of cell differsfrom the myoblasts usually met with in other species, or atany rate in the species which I have hitherto examined,chiefly in the denser chai'acter of the nucleus and its shape.

These cells, however, have the same situation as the myo-blasts in other species, namely, the median zone, midwaybetween the outer and inner limiting membranes of the sucker.

The second variety of cell (fig. 14, D z s ) is that identifiedby Jacoby as the cells which Schwarze1 considered as " Resteder urspriinglichen Bildungszellen." These are the cellsmarked "a z" in Jacoby's figures, and they occur chiefly,if not exclusively, round the aperture of the sucker. They

1 " Die postenvbryonale Entwictlung der Treinatoden," in ' Zeitsch. f.wiss. Zool.,' xliii (1886), p. 54.

462 WILLIAM NICOLL.

are large, rounded, oval cells, measuring -045 by "03 mm.They present a distinct cell wall, loosely granular contentsand a small, dense nucleus, measuring '006 mm. The nucleusstains dark red and the cell contents light purple withhsemalum-eosin. Jacoby's opinion of these cells is highlyimprobable. In reality they appear to be true cutaneousglands. Their marked resemblance both in shape andstaining properties to the true subcutaneous glands, whichin this species occur not only in front of, but also behindthe ventral sucker, cannot be ignored. . This, together withtheir distinctly marginal situation, if not a positive proof oftheir glandular nature, is at least strong evidence in favourof such a supposition. In addition it should be noted thatthese cells are smaller and less numerous in the oral suckerand are entirely absent from the pharynx.

The third variety of cell really consists of at least threedifferent kinds. The first of these (fig. 14, j? z) is confinedto the outer zone, i.e. immediately beneath the outer mem-brane of the sucker. Their nuclei are small, dense, roundbodies, measuring '008 mm. The nucleoli are small andinconspicuous. The cell-body is usually fairly definite and ofgranular structure. The second kind (fig. 14, M z) occupiesthe median zone with the myoblasts. Their nuclei areinvariably oval, and measure '0115 by '008 mm. They stainlightly aud their chrotnatin granules are arranged peri-pherally. The nucleoli are always distinct. No trace ofcell-body, however, can be detected with ordinary stainingmethods. The third kind (fig. 14, i 2) lies in the innerzone. They are distinctly multipolar, and in a tangentialsection their fibrils can be seen anastomosing with eachother. The cell-body takes on a deeper hue than any of theother cells, almost purple. They measure "02 to '03 mm.,and their nuclei, which are small, dense and usually oval,measure "007 by "006 mm.

As to the function of these last three kinds of cells anyexpression of opinion would be hazardous. Many authorshave advanced theories as to their nature, but without any

STUDIES ON THE DIGENETIC TREMATODKS. 463

generally accepted conclusion. There is evidently scope forfarther investigation on the matter.

The foregoing observations apply mainly to the ventralsucker. In the oral sucker the cells are more closely packedand not so easily differentiated. It is also worth mentioningthat in some specimens the marginal cells, to which 1 haveascribed a glandular function, can hardly be distinguished.These are generally highly contracted specimens. In mostcases, however, these cells stand out with striking distinct-ness and give sections of the sucker an entirely uniqueappearance.

In spite of their large size the suckers are not particularlymuscular. The fibres are widely separated and the interspacesare filled with a large amount of loose tissue. The radialfibres have a diameter of about "001 mm. in the case ofthe ventral sucker. Two layers of circular fibi'es are presentunder both the external and internal surfaces.

The surface of the body is covered with a fairly uniformcuticle, '002--004 mm. thick; Jacoby says -0113, but that iscertainly too high a figure. There are no spines, but thecuticle is covered throughout its whole extent with curiouslittle rod-like bodies, measuring "004 by "001 mm. (fig. 13, Cu.).These are regularly arranged, close together, and stand outstraight from the surface, not sloped backwards in the mannerof spines. They ai'e purely superficial outgrowths and donot penetrate the cuticle. It is strange that no mention ismade of these by Jacoby, for their appearance is certainlyremarkable enough. It may be that they are of transitoryoccurrence, but they were present in every specimen which Isectioned. The cuticle lining the suckers and the pharynxalso shows these rod-like bodies in many specimens.

In the anterior part of the body the cuticle is thrown intonumerous small transverse wrinkles. These are not the ir-regular wrinkles so Gommonly met with in other species ; theyare fairly uniform in size, and in longitudinal section presentthe appearance of a series of regular furrows. Of this, again,no mention is made by Jacoby. In the posterior part of

464 WILLIAM N1C0LL.

the body the cuticle does not. display the same wrinkling,and it is not preseut on the dorsal surface of the body. Thelittle rod-like bodies follow the course of these wrinkles, asdo also the circular subcutaneous muscle-fibres. The longi-tudinal muscles, however, do not; their course is straightand it is evidently to their action that the wrinkling is due.

The diameters of the circular, longitudinal and diagonalmuscle-fibres are respectively about "0015 mm., *003 mm. and•004 mm., and the spaces separating them are on an average"0035 mm., '007 mm. and -008 mm. in the three cases. Theangle made by the diagonal fibres is about 135°. Themyoblasts in connection with these fibres are quite as numerousas usual.

The true subcutaneous glands are large and numerous;they occur only on the ventral surface, but they are notconfined to the anterior part of the body, as is the case inmost species. A considerable number are to be foundbehind the ventral sucker, but they cease about the middleof the post-acetabular region. They measure about -045 by•03 mm., and are rounded, oval in outline with highly granularcontents and small eccentric nuclei, "007 mm. in diameter.

A l i m e n t a r y Sys tem.—There is a short pre-pharynx, inthe wall of which well-marked circular and longitudinalmuscle-fibres are present. The pharynx has a length of•16—'21 mm.; its breadth is usually somewhat less. I t appearsto be more muscular than the suckers, for in addition to theusual fibres several equatorial fibres are present. It containsvery few cells, and these are almost entirely of the myoblasttype, situated in the .middle zone, but much smaller thanthose of the ventral sucker.

There is practically no undivided oesophagus, the bifurca-tion taking place immediately behind the pharynx, but theinitial parts of the diverticula are not lined with intestinalepithelium. Each of these parts is about "1 mm. long and•04 mm. wide. They are lined by a cuticularised membrane.The diverticula are simple wide sacs running nearly thewhole length of the body, but terminating at the posterior

STUDIES ON THE DIGENETIC 'I'REM A.TODES. 465

end of the testes. Anteriorly their width is about '2 mm.but further back they dilate to '3 mm. They are situatedjust below the dorsal surface of the body. The intestinalepithelium is exceptionally well marked. It is cubical orcolumnar iu type, but the cells are all of different sizes andshapes, projecting to various degrees into the lumen. Towardsthe posterior end of the diverticula the cells are usuallyflatter. It is evident that these cells are capable of consider-able pseudopodial movement, for they contain varyiag amountsof bile which they have ingested (fig. 14, z). The extendedcells contain a large amount of bile sui-rounded by a vacuole.As the bile becomes metabolised and absorbed the cellcontracts and the vacuole disappears. Two neighbouringcells may thus present a great contrast, one being highlyextended and packed full of bile, the other small, flat andwithout any trace of bile. From this there can hardly beany doubt that the cells actually engulph the intestinalcontents. In their extended state they may reach a lengthof '04 mm. They possess small round nuclei situated basally.The hair-like or thread-like processes so frequently describedin other species are entirely absent in this, and it appears asif the character of the epithelium and the manner of foodabsorption in this species were different from that in mostother species. Here, however, the dark-green colour of theintestinal contents renders its presence within the epithelialcells a matter of easy observation—a fact which is by no meansso easy to demonstrate in those species in which the intestinalcontents are colourless or nearly so. It appears highly pro-bable that in many cases a certain restricted pseudopodialmovement of the epithelial cells does really take place', but itis a quite as well attested fact that in many other cases nosuch movement occurs, and that the process of assimilation-of material, partially metabolised in the lumen of the intes-tine, is effected by a capillary action of the hair-like processesof the epithelial cells.

Excretory System.—The vesicle is of the Y-shaped type.The main stem is short and almost diamond-shaped, its length

466 WILLIAM NJCOLL.

being about 2 mm. and greatest breadth "1 mm. It liesbetween the two testes and bifurcates at their anterior border.The limbs pass round the sides of the ventral sucker and takeup a position immediately ventral to the intestinal diverticula.They run forward as far as the level of the pharynx, and theirends occupy a position about midway between the pharynx andthe margins of the body. The whole vesicle, both stem andlimbs, is lined by a well-marked epithelium, the individualcells of which in many cases stand out prominently and canbe easily observed (figs. 13, 14, Ex.). At other places theyare flattened and not so distinct, so that here, again, we areevidently dealing with cells which are able to change theirshape in some degree. The nuclei of these cells are oval andmeasure about '01 by '008 mm. The vesicle communicateswith the exterior by a short narrow muscular tube, aroundwhich are numerous nucleated cells. The excretory apertureis at the posterior end of the body.

Genital System.—The genital aperture is situated on alarge papilla, which is seen prominently on external in-spection. It lies immediately in front of the ventral sucker,and displaced well to the left of the middle line. At firstsight the genital sinus appears to be of great size, but this isdue to a wide expansion of the ductus ejaculatorius. Inreality the genital sinus is comparatively small..

Male Organs.—The testes are two oval bodies sym-metrically placed about midway between the ventral suckerand the posterior end of the body. Their long axes areoblique, the posterior end being nearer the middle line; theyare separated by the breadth of the excretory vesicle. Theyare distinctly ventral in position, lying under the ends of theintestinal diverticula. Their average dimensions are '45 by•19 mm., and the thickness equals the breadth. The vasdeferens arises from a little nodule about the middle of theirinner surface.

The vasa deferentia unite in a small bipartite vesiculaseminalis, both parts of which are enclosed within the cirrus-pouch. Jacoby failed to note this bipartite condition, but

STUDIES ON THE D1GKNETIC TRJSMATODKS. 467

there is no doubt it invai'iably occurs. The posterior part isthe smaller of the two. Eaoh has a length of about -085 mm.;the breadth, which is capable of great variation, is respec-tively '06-'ll mm. and •(M-'OS mm. The walls are muscular,and an epithelial lining with a few large nuclei can be observed.The pars prostatica is exceedingly well developed, and, in fact,occupies the largest portion of the cirrus-pouch. It has, asrepresented in Jacoby's figure, a bulbous shape, narrowedsomewhat at its junction with the vesicula seminalis. Itslength is '18 mm. and greatest breadth -13 mm. Its wall ismuscular and it is lined by a distinct epithelium with ovalnuclei, measuring -0096 by -0057 mm. The lumen is almostentirely filled by long string-like masses of prostatic secretion,which lie, like so many filaments, parallel to each other, andare directed out towards the ductus, into which they project.The prostatic cells occupy a large part of the cirrus-pouch,surrounding the pars prostatica and the vesicula seminalis.A few are also found around the ductus. Their nucleimeasure •OOS-'Ol mm. Amidst the prostatic cells severallarge myoblasts or ganglion cells occur. They are distin-guished by their much larger nuclei ("012 mm.) and differentstaining reaction. The pars prostatica passes into a wide(•11 mm.) ductus ejaculatorius, of compai-atively short length.Its wall has an irregular outline, being crumpled up in some-what the same manner as in Brachycladium oblongum,but not nearly to the same extent or so regularly. At firstsight it might be mistaken for the sinus genitalis, and itcertainly offers a contrast to the long narrow ductus found inthe majority of Distomids. It is doubtful if it functions asan eversible cirrus, but if so it evidently cannot be evertedto any great length. It was not everted in any of my speci-mens, and Jacoby makes no mention of having seen it in sucha condition. The extreme prominence of the genital papillamay be an adaptation to compensate for the shortness of thecirrus. The walls of the ductus have the usual structure, butare unusually thick. The lining consists of a thick meta-morphosed epithelium easily distinguished from the cuticular

468 WILLTAM NICOLL.

lining of the sinus genitalis. A small number of " Begleit-zellen " surround the ductus.

F e m a l e Organs .—The ovary is situated on the right sideof the body immediately in front- of the testis, and justbehind the ventral sucker. Its shape is not " kegelformig,"as Jacoby describes it, but multilobate, the lobes havingapparently no uniform arrangement. This confirms Stafford'sobservation. I t is elongated in a direction parallel to thelong axis of the testis, alongside which it lies, and it appearsto be a little less than the testis in size. The oviduct arisesfrom its anterior surface and passes behind the ventral suckertowards the dorsal surface. I t dilates somewhat beforegiving off Laurer's canal, and then bends forwards to receivethe yolk-duct and pass into the ootype. Laurer's canal is ntube of about -02 mm. diameter, which- runs with severalsmall convolutions to open on the middle line of the dorsalsui'face on the level of the posterior border of the ventralsucker, or a little in front of that. I t is surrounded through-out its whole course by numerous small cells. There is notrue receptaculum seminis.

The yolk-glands are very limited in extent. They areexclusively lateral, lying to the outer side of, or even slightlyventral to, the ventral sucker. They extend from a little infront of the ventral sucker to near its posterior border.The follicles are few and of small size, and the cells liave agreat affinity for htematoxylin stains. The yolk-ducts runback alongside the intestinal diverticula, and unite in a smallmedian receptacle situated at the level of the anterior endof the testes.

Around the ootype and oviduct there is a fairly compactshell-gland of small size, but with numerous cells, the bodiesof which do not stain readily, but the nuclei are very pro-minent. The latter are oval and about "005 mm. in size.The ootype passes forwards into the uterus, which describesnumerous convolutions dorsal to the ventral sucker. Thevagina runs straight along the anterior surface of the ventralsucker and opens into the'geuital sinus. The initial part of

STUDIES ON THE DIGENETIO TREMATODES. 469

the uterus (about a third of its length) is filled withnumerous sperms, and functions as a receptaculum seminisuterinum. The ova are moderate in number and of smallsize. They are narrow oval in shape, with thick, tough shell,and measure "0424 by "0231 mm.

Fellodistomum agnotum n. sp., PI. 10, fig. 15.

Among the Distomids which were obtained from thegall-bladder or the adjoining part of the duodenum ofAnarrhichas lupus, there occurred a few which resembledFellodistomum fellis so closely that they were includedalong with it. On later and more careful examination,however, they showed features which rendered their specificdistinction comparatively easy. My attention was firstdirected towai'ds these specimens in the course of investigatingthe size at which Fellodistomum fellis attained maturity.It was rather disconcerting to find that some small specimenshad numerous ova, while other larger specimens were quiteimmature. As events have proved, the smaller specimensbelong to a distinct species.

Under these circumstances it is difficult to say what theexact habitat of this new species is. As far as- myrecollection goes, however, these were the specimens whichoccurred in the duodenum, and the true Fellodistomumfellis is apparently confined to the gall-bladder. Unfor-tunately no further opportunity has offered of confirmingthis. The new species displays the same gx*een-colouredintestinal diverticula so characteristic of Fellodistomumfellis, but this might easily be due to bile ingested in theduodenum.

The chief diagnostic features of the new species are themore elongated body, smaller and less prominent ventralsucker, the forward position of the yolk-glands, and thebackward prolongation of the uterus. It is much lessnumerous than F. fellis in the proportion of 1 to 30.

The largest specimen had a length of 3"3 mm. and a

470 WILLIAM NICOLL.

breadth of '87 niin. Other specimens Avere not quite soattenuated, but the breadth is rarely more than one thh'd ofthe length. Immature specimens were found up to l"05 mm.in length. The body usually tapers considerably towardseach end. The oral sucker measures "34 mm. and the ventralsucker "51 mm. in a specimen 3 mm. long. The proportion isconstantly 2 : 3 instead of 1 : 2 as in F . f e l l i s . Both suckersare globular. The ventral sucker lies a little in front ofthe middle of the body.

The alimentary system resembles that of F . fe l l i s . Thepharynx is somewhat smaller—'15 by "12 mm. The oesophagusis practically absent. The diverticula extend along thesides of the body and terminate at the posterior border ofthe testes, therefore at a considerable distance from theposterior end of the body. This feature is evidently sharedby the genus in common with the genus S t e r i n g o p h o r u s ,although it is not apparent at first sight in the case of F e l l o -d i s t o m u m fe l l i s , in which the testes are placed very nearthe posterior end of the body.

The excretory system corresponds with that of F . fe l l i s ,but the main stem of the vesicle is much elongated.

The genital apertni'e is placed on a prominent papillain the same situation as in F . fe l l i s , and the cirrus-pouch has the same structure. The testes are situated notfar behind the posterior border of the ventral sucker, and ata considerable distance from the posterior end of the body.They have the same shape and disposition as in F . f e l l i s .The ovary has also the same situation. The yolk-glands,however, He entirely in front of the ventral sucker andextend along the sides of the body from the anterior borderof the sucker to the level of the pharynx or intestinal bifurca-tion. They form a broader and more compact group than dothose in F . f e l l i s . The uterus describes a few windings infront of the testes, then runs back between them very nearlyto the posterior end of the body. In this part it forms asingle descending and ascending loop with little or no con-volution. On again reaching the level of the ovary it makes

STUDIES ON THIO DIGENETIO TREMATODJSS. 471

several irregular convolutions dorsal to the ventral suckerand thence proceeds to the genital aperture. This backwardprolongation of the uterus forms a ready means of distinguish-ing the species with the naked eye from F . fellis. The ovaare somewhat larger than those of the latter species, measuringabout -048 by -024 mm.

For the genus Fellodistonium, which Stafford hassomewhat scantily characterised, the following definition maybe offered :

Small to middle-sized forms with thick fleshy body, sub-cylindrical, tapering more or less towards each end. Cuticle-thick and rough, but without spines. Oral sucker sub-terminal, simple. Ventral sucker about the middle of thebody, larger than oral sucker, globular. Pharynx small,pre-pharynx short, oesophagus very short or absent. Divei"-ticula, simple wide sacs terminating a little behind the testes.Excretory vesicle Y-shaped, the bifurcation taking placebehind the ventral sucker and the limbs stretching far intothe neck. Genital aperture situated on a prominent papillato the left of the middle line immediately in front of theventral sucker. Small genital sinus. Testes symmetrical,n moderate distance behind the ventral sucker. Cirrus-pouch compact, bulbous. Vesicula seminalis small, bipartite-Pars prostatica well maz*ked; ductus ejaculatorius short, wide,with walls thrown into irregular folds (in the retractedstate). Ovary niultilobate, situated just in front of theright testis. Receptaeulum seminis absent; Laurer's canalpresent. Yolk-glands lateral, of very limited extent. Initialpart of uterus functions as receptaculum seminis uterinum.Uterus restricted in extent, either confined between thetestes and the genital aperture, or with a loop passing back-wards between testes to the posterior end of the body. Ovasmall, thick-shelled, measuring *04—"05 mm. by -02—'025 mm.

Type.—Fellodistomum fellis (Olsson, 1868) = ? F .incisum (R.) Stafford. Including also F . agnotum n. sp.

Both Stafford and Odhner have noted a close resemblancebetween this genus and the genus Ster ingophorus Odhn.,

VOL. 53 , PAKT 3 . NEW SBBIES. 33

472 WILLIAM NICOLL.

1904 ( = L e i o d e r m a Stafford, 1904), of which the type isSt. f u r c i g e r (Olss., 1868). The latter genus has been effi-ciently chai'acterised by Odhner.1 The two genera showunmistakable evidences of relationship, and they represent atype of structure distinct from that of any other sub-familyof the PROSOSTOMATA. They may therefore be regarded as thenucleus of a separate sub-family as already indicated byOdhner, and for this I propose the name FELLODISTOMINJEn. subfarn., with the following provisional diagnosis :

Under middle-sized to middle-sized forms with fleshy body.Cuticle unarmed. Ventral sucker larger than oral sucker,situated about the middle of the body. Alimentary canalwith short or nearly absent oesophagus, and diverticula nocextending much beyond the level of the testes. Excretoryvesicle Y-shaped, the fork taking place behind the ventralsucker and the limbs extending well into the neck. Genitalaperture a short distance in front of the ventral sucker, medianor to the left side. Testes symmetrical, lateral, not farbehind the ventral sucker. Cirrus-pouch compact, bulbous,containing a small bipartite vesicula seminalis, a well-markedpars prostatica, and a short, wide ductus ejaculatorius. Ovaryin front of right testis, multilobate. Receptaculuni seminisabsent (or present sometimes), Laurer's canal present. Yolk-glands limited in extent, lateral, on each side of the ventralsucker. Yolk-reservoir median behind ventral sucker. Uterusmore or less convoluted, confined between testes and genitalaperture or extending back between testes into the posteriorpart of the body. Ova fairly numerous, measuring about *04—•06 mm. by -02--03 mm.

Type, F e l l o d i s t o m u m (Stafford, 1904).Including also S t e r i n g o p h o r u s , Odhner.

Genus, S t e r i n g o p h o r u s Odhner, 1904.Ster ingophorus cluthensis n. sp., PL 10, fig. 16.This species was found fairly abundantly in the upperi « Trematoden d. arktischen Gebietes," in 'Fauna Arctica.'iv (1904),

p. 309.

STUDIES ON THE DIGBNKTIC TKEMATODtiS. 473

reaches of the intestine (duodenum and casca) of Pleuro-nectes microcephalus, the lemon-dab, from the Firth ofClyde. It differs in several respects from St. furciger(Olss.), which is found so commonly in many Pleuronectidfishes in the North Sea.

In life the animal is capable of great extension and con-traction, but on being killed or on being allowed to die in itsnatural habitat it assumes a fairly regularly oval outline,always more pointed towards the anterior extremit3r. It isconsiderably flattened and has a rather delicate, transparentappearance. Living specimens have a distinctly reddishcolour, not so deep as that of St. furciger.

The length is 1*5-2 mm., but none of iny specimens seem tobe fully mature, so they may attain a larger size. Thebreadth is about two fifths of the length—"6—"8 ram. Cuticleunarmed. The oral sucker invariably lies a short distancefrom the extreme anterior end, and it is usually elongated inthe long axis of the body. It measures about "22 by '15 mm.The ventral sucker is almost exactly twice as large, itsdiameter being "44 mm. in a specimen of 2 mm. length. Itis situated a little behind the middle of the body, and it thisrespect it differs from the position in St. furciger, in whichit is in front of the middle of the body.

The pharynx is immediately behind the oral sucker andmeasures '085 mm. in diameter. The oesophagus is twice aslong as the pharynx, sometimes slightly more, sometimes alittle less than that. This feature, again, distinguishes thespecies from St. furciger, in which the oesophagus is aboutthe same length as the pharynx. The diverticula are simpleand extend a little beyond the testes, but not so much as inSt. furciger.

The excretory vesicle is perhaps the most obvious diagnosticfeature. It is Y-shaped, but the unpaired portion is veryshort, so that it sometimes appears almost V-shaped. Thepaired limbs extend forward to the level of the pharynx. Itis distinctly mapped out by the refringent nature of itscontents, but is not so conspicuous as in St. furciger.

474 WILLIAM NIOOLL.

The genital aperture is situated just behind the intestinalbifurcation, to the left of the middle line, although not much.The testes are symmetrically situated midway between theventral sucker and the end of the body. They are somewhatfurther back than in St. f u r c i g e r . Their long axes arealways a trifle oblique, the anterior end being directed out-wards. They measure "15 by *12 mm. The cirrus-pouch isbulbous or nearly globular, and lies entirely in front of theventral sucker. I ts internal structure is the same as that ofSt . f u r c i g e r , but the pars prostatica is longer and narrower,as are also the two parts of the vesicula seminalis.

The ovary is situated immediately in front of the righttestis. I t is multilobate, but very small. The yolk-glandsare much nioi-e extensive than in St. f u r c i g e r . They extendfrom the testes forward to the level of the middle of the cirrus-pouch, i . e . well in front of the ventral sucker. In St. fur-c i g e r they do not reach the anterior border of the sucker.The transverse yolk-ducts run obliquely backwards to uniteat the level of the anterior border of the testes in a smallmedian yolk-reservoir. In none of my specimens was theuterus very voluminous. A few convolutions were foundbetween the testes and stretching back to the posterior endof the body. The terminal part runs forwards on the left sideof the ventral sucker to open into the sinus genitalis. Theova are not particularly thin shelled, and measure '044—-056by -028--032 mm.

The chief diagnostic features of this species may besummed up as follows : Post-acetabular region shorter thanpre-acetabular region. (Esophagus twice as long as pharynx.Excretory vesicle nearly V-shaped. Yolk-glands extendingin front of ventral sucker.

The introduction of this species within the genus S t e r i n -g o p h o r u s involves only two modifications of Odhner'sdefinition. The words " Saugnapfe genahert" and " Stamm(der Exkretionsblase) gabelt sich zwischen den Hoden"should be deleted.

A species which bears a striking superficial resemblance to

STUDIES ON THE DIGENET1C TEEiMATODES. 475

Ster ingophorus cluthensis is Distomum pagell iv. Ben. (fMem. Acad. Roy. Belg.,' xxxviii (1871), PJ. IV, fig.17), from Spar us centrodontus. Van Beneden, unfor-tunately, gives absolutely no description of the species, butfrom his figure it seems probable that it is really aSter ingophorus sp. It differs from Ster. cluthensisin having the ventral sucker three times as large as the oralsucker, the ovary globular, the yolk-glands extending behindtestes, and the genital aperture further from the intestinalbifurcation.

It is evidently a somewhat difficult matter to differentiateSteringophorus generically from Fellodistomum. Thefeatures which require to be emphasised in the former are:(1) the presence of a distinct oesophagus; (2) the absence ofa protuberant genital papilla; (3) the situation of the genitalaperture near the intestinal bifurcation instead of close infront of the ventral sucker; and (4) the presence of a truereceptaculum seminis.1 These differences are not of greatrelative importance, and it is not at all impossible that thegenera may eventually prove identical, in which case thename Steringophorus must be regarded as a synonym ofPellodistomum.

Sub-family PLAGTORCHINA: Pratt, 1902.

Genus Plagiorchis Liihe, 1899.Plagiorchis notabilis n. sp., PI. 10, fig. 17.

To the genus Plagiorchis have already been assigned well-nigh a dozen species, one or two of which can be differentiatedfrom each other only with difficulty. They form on the wholea very homogeneous group. To these I have to add a formpossessing such well-marked features that there can be nodoubt of its specific distinctness.

1 According to Odlmer there is no receptaculnm seminis, but MissLebour (' Fish Trematodes .of the Northumberland Coast,' p. 15) hasshown that such a structure may actually exist in Steringophorusfurciger.

476 WILLIAM NIOOLL.

The species in question was first obtained on August 21st,1907, from the middle part of the intestine of An thusobscurus (rock pipit), which is by far the commonest birdinhabiting the rocks along the shore in this district. Theparasite, however, is by no means frequent, for out of elevenpipits shot during August to October only two specimenswere obtained—one adult and one immature. A point ofinterest is that the two birds from which those specimenswere obtained contained several other parasites, in particulartwo species of Spelotrema and a number of Cestodes. Theother birds contained only a few examples of Spelotremaclaviforme and an occasional Cestode. Several other rock-frequenting bii'ds. e. g. Saxicola cenanthe and Mota-cilla flava, were examined in the hope of finding morespecimens of the parasite, and towards the middle of Octoberanother single example was found in the intestine of Mota-cilla. This second example did not entirety agree with thefirst, but at present they may be l'egarded as one and thesame species. To avoid detailed comparison the -specimenfrom Anthus will first be described, and the main featuresof difference in the specimen from Motacilla will then beindicated.

The general shape is that common to the genus. Thelength is 1*6 mm.; the breadth is fairly uniform—•52-"57 mm.Almost the whole surface of: the body is covered with minutestraight spines which have the peculiarity that they justbarely pierce the cuticle. This feature is shared by theother members of the genus, and would appear to be charac-teristic.

The oral sucker is not quite at the extreme anterior end ofthe body, but is a short distance from it. Its length is slightlygreater than its breadth, and it has an elongated slit-likeaperture. This again appears to be characteristic of thegenus. In this species the aperture is slightly expandedposteriorly and narrows to a fine point at the anterior end.The sucker measures "20 by "18 mm. The ventral sucker isglobular, with a circular aperture, and measures only -16

STUDIES ON THE DIGENETIO TKEMATODES. 477

mm. It is situated at the end of the first third of the bodylength.

The pre-pharynx is extremely short; the pharynx is broadiind measures "07 by "09 mm. There is practically nooesophagus and the simple straight diverticula extend towithin a short distance of the posterior end of the body.

The genital aperture lies immediately in front of the ventralsucker, median or very slightly to the left. The cirrus-pouch bends round to the right side of the ventral sucker.It differs in shape from that of most members of the genus,approaching most nearly that of Plagiorchis (Lepo-clerma) ramlianus (Lss.). It is short and stout and doesnot extend beyond the posterior border of the ventral sucker.It is somewhat pointed at its proximal end, where it receivesthe vas deferens. Thevesicula seminalis is oval with only theslightest trace of a constriction, and measures "14 by "07 mm.The prostate cells are fairly numerous, surrounding thefirst half of the ductus ejaculatorius and pars prostatica. Inthis specimen the ch-rus was exserted as a long, narrow,sinuate filament, pointed at the end and measuring "25 mm.in length. The vagina runs up to the genital aperture on theleft side of the ventral sucker. The arrangement of thegenital glands is the same as that in the other members ofthe genus. The anterior testisis *20 mm. behind the ventralsucker, and the posterior testis is '35 mm. from the posteriorend of the body. Between the testes there is a space of• I mm. They are about equal in size, measuring 25 by•16 mm. They, are elongated in the long axis of the body,and they lie to the inner side of the intestinal diverticula.

The ovary is situated further forward than in any otherspecies of the genus. It lies on the right side with itsanterior border contiguous with the end of the cirrus-pouch,or on the level of aperture of the ventral sucker. It alsolies to the inner side of the right intestinal diverticulum, butslightly overlaps it. It is longitudinally oval and measui-es*16 by '12 mm. From its inner side the oviduct arises andruns towards the middle of the body, where it gives off

478 WILLIAM NIOOLL.

Laurer's canal. No receptaculum seminis could be made outwith certainty.

The yolk-glands are almost entirely confined to the sidesof the body and extend from the pharynx to the posteriorend. They do not unite in the middle line posteriorly, but afew follicles stretch across the body just behind the pharynx.The intestinal diverticula are overlapped to a slight extent,especially posteriorly. The transverse yolk-ducts pass alittle in front of the anterior testes to unite in a smallreservoir.

The uterus is confined to the posterior half of the bodyand does not overlap the intestinal diverticula. Its course istypical of the genus, but it diffei-s in being more voluminousin front of the posterior testis than behind it. I t does notoverlap the testes. The ova are not very numerous; theymeasure "031 by '019 mm. and have a bright yellow shell.

The chief diagnostic features of this species are thereforethe short cirrus-pouch and the forward position of theovary.

The specimen from M o t a c i l l a f l a v a was smaller andslightly narrower; length 1*4 mm. Oral sucker *17 by•16 mm.; aperture *09 by '03 mm.; thickness of wall '03mm. Ventral sucker two fifths of the body length fromthe antei-ior end, size '14 by "13 mm.; aperture circular.Phai-ynx '054 by -069 mm. Spines '0096 mm. long.

Cirrus not completely exserted. Vesicula seminalis dis-tinctly bipartite, with a small anterior and a larger postei'iorpar t ; combined length of the two parts "066 mm. Thedistinct bipartite condition of the vesicula in this specimenis one reason for doubting if it is really identical with thespecimen from A n t h u s o b s c u r u s . Possibly the differencein the state of exsertion of the cirrus may account for thevariation in the vesicula.

The genital glands have much the same situation as before,but the posterior testis is only "12 mm. from the end of thebody and the anterior testis "13 mm. behind the ventralsucker. They are smaller and not so elongated, "17 by

STUDIES ON THE D1UBNET1C TJJBAIATODJSS. 479

•15 mm. and "19 by "15 mm. respectively. The ovary is alsosmaller—"115 by "105 mm. The uterus is more voluminousbehind the posterior testis and overlaps the testes to a slightextent. The ova are brownish-yellow and measure "0308by '0193—"0212 mm. The length is practically invariable, butone abnormally large ovum was observed in the posterior loopof the uterus, measuring '0327 by '0212 mm. The average sizemay be taken as "031 by '021 mm. They are not truly ellip-soidal, there being a slight flattening on one side, which pro-bably accounts for the variation in the breadth. The shell has athickness of '0008 mm. The vagina lies on the right side of theventral sucker and extends as far back as its posterior border.I t is marked off from the uterus by a distinct constriction.Its diameter is '015 mm. and its walls are "006 mm. thick.

The yolk-glands are less voluminous than in the firstspecimen. They are entirely lateral and extend only a shortdistance in front of the ventral suckev. This might beascribed to imperfect development, but as both specimenswere fully mature it seems more reasonable to allow thatsome variation may occur in the extent of the yolk-glands.In this respect Braun,1 in discussing the distinction betweenP l . e l e g a n s (R.) and P I . c i r r a t u s (R.), remarks that muchweight cannot be placed on the relative extent of the yolk-glands, for they vary even in examples from the same host.

This specimen differs from the first mainly in the conditionof the vesicula seminalis, the extent of the yolk-glands, andthe size of the genital glands. Until more material is avail-able it is impossible to say whether these features are ofspecific importance or merely variations.

The species which follow are introduced mainly for thepurpose of presenting figures which were omitted from aprevious paper.3 Little opportunity has offered of making

1 " Fascioliden der Vogel./' in • Zool. Jakrb.,' syst. xvi, pp. 37-55, pi.iii, figs. 25-34a.

3 " Observations on the Treniatode Parasites of British Birds," in• Annals and Mag. Nat. Hist.' (7), xx (1907), pp. 245-271

480 WILLIAM NICOLL.

fresh investigations in connection with these species, and thenotes which are herewith given are only such as to correct afew obvious errors.

Sub-family, MICUOPHALHN.M Ward, 1901.

Genus, Spe lo t rema Jagersk., 1900.

This genus includes the species Sp. pygmseum (Levin.),Sp. claviforme (Brandes) Mihi., Sp. simile Jagersk., andSp. excel lens Mihi. Afifth species, namely, Sp. fer ia tumMihi, has been found to belong to the nearly allied genusLevinseniel la . The genus may require to be furtherrestricted to three species, for Sp. claviforme (Brandes)Mihi is only doubtfully distinct from Sp. pygmaeum. Thecharacters of the four species may be briefly summarised asfollows:

Spelot rema pygimeum (Levins.) Odhn.

Odhner, "Treinatoden des arktischen Gebietes" in ' FaunaArctica,' iv (1904), pp. 315-317, fig. 1, 2A.

Length "3—'5 mm. Maximum breadth *2—"3 mm. Club-shaped. Diameter of suckers about "04—-05 mm., but oralsucker always slightly larger than ventral sucker. Ventralsucker a third of the body length from the posterior end.Intestinal diverticula reaching" posterior border of ventralsucker. Genital body only half the breadth of the ventralsucker. Ductus ejaculatorius short and direct. Testes com-paratively large. Uterus fairly voluminous, but not obscuringtestes. Ova •021-"023 by "012 mm. Habitat, Somater iamollissima, Somater ia spectabi l is , Oidemia nigra,and Oidemia fusca.

Spe lo t rema claviforme (Brandes) Mihi (PI. 10, fig. IS).

Nicoll, "Trematode Parasites of British Birds" in 'Annalsand Mag. Nat. Hist./ (7) xx, (1907), pp. 254-255.

Length 2-"4 mm. Maximum breadth 'lS-^O mm. Club-

STUDIES ON THE DIGENETIC TBEMATODES. 481

shaped. Oral sucker always distinctly larger than ventralsucker; diameters '035-'04 mm. and "03—"035 mm. respectively.Ventral sucker less than a third of the body-length from theposterior end. Intestinal diverticula short, wide apart, anddo not reach the level of the ventral sucker. Genital bodyless than half the diameter of the ventral sucker. Ductusejaculatorius short and direct. Testes not prominent. Uterusvoluminous, obscuring the testes aud extending slightly infront of ventral sucker. Ova •020--024 by -011-014 mm.Habitat, Pelidna alpina, ^Egialitis hiaticula, Anthusobscnrus,1 Numenius arquata,1 Motacilla flava,1

Larus ridibudns.1

Spelotrema simile Jagersk.•Jiigerskiold, " Levinsenia pygmaia Levinsen, etc.," in

' Centralbl. f. Bakter.,' Abth. i, Bd. xxvii (1900), pp. 732-740.Length "4—-6 mm. Maximum breadth -2 mm. "Biscuit-

shaped." Oral sucker slightly smaller than ventral sucker,diameter '05—"06 mm. Intestinal diverticula reach posteriorborder of ventral sucker. G-enital body has diameter at leasttwo thirds that of the ventral sucker. Ductus ejaculatoriuslong and convoluted. Uterus not usually voluminous, notobscuring testes or yolk-glands. Ova pale, measuring -023—•026by "011—-013 mm. Habitat, Larus argenta tus , Larusfuscus, Larus ridibundus.1

Spelotrema excellens, Mihi (PI. 10, fig. 19).Nicoll, f Annals and Mag. Nat. Hist.,' (7) xx, (1907), pp.

248-251.Length "7-1 "4 mm. Maximum breadth "35—-50 mm. Club-

shaped. Oral sucker slightly larger than ventral sucker;diameter <06-'085 mm. Intestinal diverticula terminate atthe level of the centre of the ventral sucker. Genital bodynearly as large as ventral sucker. Ductus ejaculatorius shortand straight. Uterus very voluminous, obscuring testes,but not extending in front of ventral sucker as a rule. Ova

1 New hosts

482 WILLIAM NICOLL.

very numerous, measuring •023->025 by 'OIO-'OIS mm.Habitat, Larus argentatus.

Sj Levinseniella Stiles, 1902.The species of this genus, uamely L. brachysoma (Orepl.),

L. pellucida Jagersk., and L. propinqua Jagersk., havebeen efficiently described by Jagerskiold.1 The specieswhich I have described under the name Spelotremaferiatum n. sp.2 must be considered as a mixture of two ormore of the above mentioned species or of some hithertoundescribed species of the same genus. I found the speciesoriginally in Htematopus ostralegus, and was struck withits resemblance to Distomum brachysomum Orepl., butwas led astray by Villot's ti-ansposed representation3 ofCreplin's species. Jagerskiold's elucidation of the truestructure of that species has enabled me to identify myspecimens as Levinseniella brachysoma or some nearlyrelated species.

At the time of describing the species "Spelotremaferiatum," I entertained great doubt as to the actualidentity of my specimens from Vanellus and Hfematopuswith those from Pelidna and -<55gialitis. This doubt hasnow given place almost to a certainty that they are distinctlydifferent, for the former, although quite as large as the latter,were in every case decidedly immature and pale in. colour,while the latter contained numerous ova and were of a moreor less brownish colour. According to Jiigerskiold, Hsema-t o p u s harbours a species distinct from that inhabitingvEg ia l i t i s , T o t a n u s and P e l i d n a . This would appearto solve the difficulty with regard to my specimens, butunfortunately I cannot entirely reconcile my own observa-tions with Jagerskiold's descriptions. For instance, the brownpigmentation of the body and the intensely black mapping

1 " Zur Kenntniss der Treniatodengattung Levinseniella,' in ' Zool.Studien tilliignaae,' Prof. T. Tullberg, 1907, pp. 133-154.

- ' Annals and Mag. Nat. Hist.,' (7), xx, pp. 251-253.3 ' Ann. d. Sciences Nat.,' (6), viii (1879), pp. 22-24, pi. v, fig. 7.

STUDIES ON THE DIGHNBTIO TllEMATODES. 483

out of the excretory system are not mentioned by JagerskioldI have endeavoured to utilise the table of specific differencesgiven by Jagerskiold1, but without any consistent result.From the point of view of the compai'ative length of thepre-pharynx, for instance, my specimens from Totantis andVanellus ought to be regarded as L. propinqua but theidentity is not confirmed in other respects. For the present itseems the safest plan to refer my specimens from Pelidna,jiEgialitis and Totanus to Levinsinella brachysoma(Crept.), while those from Hasmatopus and Vanellusmust be regarded as Levinsinella sp. inquir. The mostcurious feature about the latter is the fact that on no occasiondid I find a fully mature specimen, although I examinedseveral of these birds at different times. In addition to theforegoing hosts I have also to add Numenius arquata, inthe caeca of which I have found a Levinsinella sp.,probably L. brachysoma.

Sub-family TocotreminEe Jagerskiold, 1902.

Genus Tocotrema Looss, 1899.

Tocotrema jejunum Mihi (PI. 10, figs. 20 and 21).

I have not yet again met with this species. Two figuresof it are shown here, one i*epresenting what may be regardedas the normal shape, the other that in which it was usuallyfound.

Genus Oryptocotyle (Liihe) Mihi, 1907.

Cryptocotyle concava (Crepl.) (PI. 10, figs. 24 and 25).

My revised definition of this genus requires alteration in, atleast, one point. From a rather poor series of sections Ihave been able to make out that the genital sucker containsa distinct plug-shaped body ("kegelformiger Korper"). Itis, however, much smaller than the corresponding structure

1 Op. cit., p. 147.

48-4 WILLIAM NICOLL.

in T o c o t r e m a . This fact removes an important point ofdistinction between the genera O r y p t o c o t y l e and Toco-t r e m a , but sufficient differences remain to keep themgenerically separate.

In my previous note on Looss's sub-family Ooeno-goniininas ( H e t e r o p h y i u t e ) , I arrived at practically thesame conclusion as Jagerskiold did in a paper1 which I hadnot at that time seen. Jagerskiold separates the sub-familyToco t reminae from the CoenogoniniinEe, including in theformer the same genera, with the exception of C r y p t o -co ty l e , as I did later. He also ventures the suppositionthat the M i c r o p h a l l i n a e are more or less nearly related tothe Tocotreminae-Coenogoi i iminse group, and this seemsnot at all unreasonable. Their relation to the B r a c h y -coeliina3 is undoubtedly much more remote, and my sugges-tion of a natural family to include all these forms was certainlypremature if not erroneous.

Sub-family G-ymnophall inse Odhn., 1904.

Genus G y m n o p h a l l u s Odhn., 1900.

G y m n o p h a l l u s d a p s i l i s Mihi (PL 10, fig. 24).

An explanation of the curious condition of the ova in thisspecies is suggested in a note by Looss,3 who has met with ananalogous condition in several other species, and ascribes itto an imperfect functioning of the ootype. The malformedova may therefore in a sense be regarded as abortive. Ihave since noted the condition in one or two other species,but only in isolated individuals, and never with, the sameremarkable frequency as in G y m n o p h a l l u s d a p s i l i s .

Sub-family M a r i t r e m i n s e provis.

Genus M a r i t r e m a Mihi, 1907.

I have at pi'esent nothing further to add to the descriptions1 " Scaphanocephalus expansus (Crepl.), etc.," in ' Results of

Sweclisli Zool. Exped. to Egypt,' 1901, No. 23.: "Treniatoden sus Seeschildkroten," in'Zool. Jahrb. Syst.,' xvi,p. 475.

STUDIES ON THE DIGKNETIO TREMATODJSS. 485

of the three species of this genus. They are represented herein PI. 10, figs. 25-27.

Dr. Jtigerskiold has just sent me a papei* dealing with thegenera Spelotrema and Mari t rema (in ' Centralbl. f.Bakt., etc., I Abt. Originale,' Bd. xlviii, pp. 302-317). Hisdescription of Spelotrema excellent appears to agreevery closely with mine. The elongated shape of the ovaryis certaintly not a constant feature of the species, nor is thelarge size of the vesicula seminalis, on which Jagerskiold layssome weight. It is an organ which is capable of not a littlevariation in size at different times in the same animal.

With regard to the genus Maritrema, Jiigerskiold's twonew species appear to be quite distinct from those which Ihave previously described. He is correct in drawing attentionto the disposition of the yolk-glands. The genus, as Jagers-kiold points out, shows a i-elationship to the MICEOPHALLINJ<:,but it is certainly not close enough to permit of its beiugincluded in that sub-family.

EXPLANATION OF PLATES 9 AND 10.

Illustrating Dr. William NicolFs paper entitled "Studies on theStructure and Classification of the Digenetic Trematodes."

The following letters apply to all the figures :B.S. Ventral sucker. C.B. Cirrus-pouch. JD.E. Ductus ejacula-

torius. D.St. Yolk-glands. Ex. Excretory vesicle. / . Intestinaldiverticula. K.St. Ovary. L.C. Laurer's canal. M.S. Oral sucker.Oe. (Esophagus. Ov. Ova. P.O. Genital aperture. PA. Pharynx.P.Ph. Pre-pharynx. P.Pr. Pars prostatica. Pr. Prostate glands.Ti,T.2. Testes. U.S. Receptaculuni seminis. S.D. Shell-gland. JJt.Uterus. Vg. Vagina. V.S. Vesicula seminalis.

FIG. 1.—Stephanophiala laureata (Zed.). Ventral view, x 35.V.P. Ventral papilla.

486 WILLIAM NICOLL.

FIG. 2.—Steph. laureata. Longitudinal section of antei-ior end,nearly median. X 85. V.P. Ventral papilla. D.P. Dorsal papilla.«. Myoblast.

FIG. 3.—Steph. laureata. Cirrus-pouch and vagina. Somewhatdiagrammatic. X 270. <£. Male genital aperture. ?. Femaleaperture.

FIG. 4.—Steph. laureata. Transverse section, yolk-follicles. X270. P.C. Parietal cell. C.C. Central cell. D.G. Yolk-duct. Y.C.Yolk-cell.

FIG. 5.—Steph. laureata. Immature specimen, x 60. E.S. Eyespot.

FIG. 6.—Brachycladinm oblongum (Brn.). Shell-gland complex.Transverse section. K.G. Oviduct. D.G. Yolk-duct. Cu. Cuticle.D.R. Yolk-reservoir. V.D. Vas deferens. U.S. Ut. Receptaculuniseminis uterinum. Oo. Ootype.

FIG. 7. — Bracliycladium oblongum. Longittidinal mediansection through genital aperture. X 60.

FIG. 8.—Bracliycladium oblongum. Longitudinal median sectionthrough anterior end, showing pre-pharyngeal pouch. Reconstructed.X 60. Div. Pre-pharyngeal pouch.

FIG. 9.—Lebouria idonea n. sp. Ventral view. x 50. D.R.Yolk reservoir.

FIG. 10.—Lebouvia idonea. Coronal section, anterior end. x 100.I.D. Intestinal dilatation.

FIG. 11.—Lebouria idonea. Cirrus-pouch, x 330. B.Z. " Begleit-zellen."

FIG. 12.—Lebouria idonea. Shell-gland complex. Dorsal view.X 85. K.G. Oviduct. D.G. Yolk-duct. D.R. Yolk-reservoir.

FIG. 13.—Fellodistomum fellis (Olsson). Longitudinal sectionthrough dorsal surface and intestinal diverticuluin jxist in front ofventral sucker. X 80. Cu. Cuticle with rod-like bodies. Ep. Intestinalepithelial cells containing masses of bile (Z.).

FIG. 14.—Fellodistomum fellis. Transverse section throughcentre of ventral sucker, x 75. CM. Circular muscle-fibres of sucker.B.Z. Subcutaneous gland cells. D.Z.S. Gland cells of the sucker. G.Z." Grosse zellen" (myoblasts ?). I.Z. Cells of the inner zone. M.Z.Cells of the median zone. P.Z. Cells of the outer (peripheral) zone.

FIG. 15.—Fellodistomum agnotuin n. sp. Ventral view, x 35.FIG. 16.—Steringophorus cUithensis n. sp. Ventral view. X 55.FIG. 17.—Plagiorchis notabilis n. sp. Ventral view, x 55. C.

Cirrus.

STUDIES ON THE DIGENBT1C TftE&lATODBS. 487

FIG. 18.—Spelotrema elaviforme (Brandes). Ventral view, x200. G.S. Genital sucker.

FIG. 19.—Spelotrema excellens Mihi. Ventral view. X 130.G.S. Genital sucker.

Fia. 20.—Tocotrema jejunum Mihi. Ventral view, x 65. G.S.Genital sucker.

FIG. 21.—Tocotrema jejunum. Ventral view. Greatly extendedspecimen, x 65. G.S. Genital sucker.

FIG. 22.—Cryptocotyle concava (Crepl.). Ventral view, x 95.G.S. Genital sucker. D.B. Yolk reservoir.

FIG. 23.—Cryptocotyle concava. Median longitudinal section.X 240. G.S. Genital sucker. Z. "Znnge." Ov. Ovum.

FIG. 24.—G-ymnopliallus dapsilis Milii. Ventral view, x 95.FIG. 25.—Maritrema gratiosurn Mihi. Ventral view, x ]10.FIG. 26.—Maritrema lepidum Mihi. Ventral view, x 100.FIG. 27.—Maritrema humile Mihi. Ventral view, x 180.FIG. 28.—Podocotyle atomon var. dispar. Ventral view, x 45.

U.D. Unpaired group of yolk-follicles. D.B. Yolk reservoir. D.G.Longitudinal yolk-duct.

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