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ONTOGENY OF EMBRYONIC BEHAVIOR I N AVES111. 'I'llli: S'I'ItUC'r~Jl~T, AND Ji:NVTRONR4ENTAJl FACTORS INIdMI1ItYO NLC: LlldlLAVLOlZ,

ZING YANG ICUONalional Central U niversi ty, Nanking, China

1 INTRODUCTIONWhile it nppen.rs to l)e n hcnlt,hy nnd promising sign that a fewbiologists and psychologists have recently manifested some inter-

F est in the stud y of embryonic and fetal behavior in various verte-b brates, it is rather disappointing that these investigators have

i almost entirely neglected the anatomical and environmentalaspects in their studies of develanmental behavior. The workof Coghill (1024, 1926, 1929 and 1930) on the behavior of th ef larva of the Amblystoma has no reference to its environmenti whatever. Those who have worked on the behavior of mam-malian fetus (Angulo (1929 and 1930), Avery (1928), Brown (1914and 1915)) Langworthy (1929)) Minkowski (1921, 1922, 1923,/ 1924 and f925), Pankrats (1930)) Swenson (1925, 1928, 1928a and1 1929), and Windle (1930)) removed the fetus from the uterusI and g:tthvl-c(I frngmcr~f.nrynforrnat,ion conccrning i ts body movc-i ments (which movements, by the ~vay, re rather pathological.

1 For detailed objections to their methods of stu dy see Kuo (C))1 without noting the effcct on behavior of the removal of the fetusfrom its normal fetal environment after the experimental delivery.i. Th at the na ture of behavior can be understood only in terms of it scausal relation with the environment should be obvious to everyone. And yet these investigators have no t felt the need of pre-i serving and understanding normal embryonic and fetal environ-! ment in their behavior studies. And it is part ly due either toE negligence or to ignorance of environmental factors tha t we, of4 late, so often find in current literature such a meaningless expres-t 245-I5

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246 ZING YANG KUO ONTOGENY O F EMBRYONIC BEHAVIOR I N AVES 247

plete, the general body form, the structure o f different organs,and the relative size and proportion of different body pa rt s arechanged from time to time as a result of development and growth.Such changes have profound effects on the modes of behavior.Unfortunntely, this nspcct of the problem of the tlevclopmcnt ofbehavior has been ~~cglcctcdl tllough considerable attcrl tior1 hasbeen recently paid by several investigators to the possible correla-tion between the development of the nervous system and thedevelopment of behavior. We shall in a later section discuss therelative importance in determining behavior between grossanntomicd changes of the body as a whole and the developmentof thc nervous system.

i From our studies on the origin and development of embryonicbehavior in birds we have gathered sufficient evidences to demon-strate tha t indevelopment behavior is ~ri ma ri ly etermined@by changes in gross cuah my , b - b y the nature of the environ-ment, and @) by the past history of behavior of the organism.The effect of the pas t history of behavior on new bchavior will bedea lt with elsewhere (see the fourth article of this series). Inthe following pages we shall present evidence concerning theeffect of s truc tura l and cnvironrncntal factors on embryonicbehavior in birds. While our studies have included both pigeonand duck embryos, besides chick embryos, the present report willbe confined to the behavior of the Iatter alone. I t must be noted,ho~vcvcr, th at there is practically no tlifI'crcncc bctwecn thepigeon or duck embryo and the chick embryo with regard to thestructural and environmental factors in determining behavior.

In view of the fact that in our investigations on the behavior ofthe bird embryo we have used several thousand eggs, it would be

sion as "pontaneous activities" as if animal activities could 1 impossible for us to report in this paper statistical details or

He ad nzovements as e.flected by str uctural cilanges. We havereported elsewhere (Kuo, I) tha t head movements are the earliestphysiological responses found in the chick embryo. The y gener-ally appear by the fourth day of incubation. Bu t in many cases,head niovcmcnt,s nrc o1)servcd as early ns the third day of incuha-tion. In the three- or four-day embryo head movements consistof lifting upward, and bending toward the breast. But from thefourth or fifth day on head lifting and head bending graduallydisappear and a new mode of head movement takes their place,namely, the turning of the head to the sides. On the fourth da y,head lifting is still the dominant response of the head althoughturning to the sides is also present in some embryos (table 1) .In the five-day embryo, the frequency and relative magnitudeand th e number of birds are decreased for head lifting bu t in-creased for side turning. In fact, the head movement of thefive-day embryo has become semicircular, which motion is thedirect result from the combination of the uplifting and side turn-ing movements of thc head. Between the sixth and ninth daysof incubation, head lifting disappears entirely (except 20 cases ofsix-day embryos, table 1) while side turning of the head has be-come the major response of the head although the bending of th ehead towards the breast is still observed occasionally.

The question is immediately raised: what causes the transfor-mation of the head movement from uplifting to side turning?The key to this question lies in the anatomical changes during thesesta.ges of development. In the three- or four-day embryo, thehead is not heavy and there is no neck. From the fifth day on theweight of the head increases enormously. Before the ten th da yit is heavier than the weight of the body, and is more tha n 50 per

appe ar without cause or without preceding stimulation. Weshall take up this question of spontaneous activities again a t theend of this paper.

In the adu lt animal changes in gross anatomyare not so apparentand profound, so t ha t t,heir effects on behavior may be somct,imes~~cgligible. 1 1 tl ~c t,I~(:rI : I , I I ( ~ , i11 L I I C y o t ~ r t ~~ , r ~ i ~ t l : l I ,:s11(:ci:~llyduring the embryonic and fetal stages, metamorphosis is not com-

individual cases; we have to be content with a somewhat sum-marized form of presentation.

The methods of studying embryonic behavior in birds have beenfully described in the first article of this series. To avoid unneces-snry rcpctition the render is rcferrcd to that article (Kuo, T ) .

STRUCTURAL EFFECTS O N EMBRYONIC BEIIAVIOR

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248 Z ING YANG KU Ocent of th e tota l weight of t.he embryo (48.6 per cent of total weighthy thc rtirltli tlny whcrc:~s t is only 18.3 per ccnt a t t,hc t h e ofhntc lii~rg, tnblc 2). 'I'hc riccllyclillicr~lt,f ~ ~ o t~~~l)ossil)lc>,o t 011c(.1111)ryoo

TADLE 1Averaged Jrequency and magnilude of head l i f t ing and head l tsrning (lo s ides) in 414chick embryos from the th ird day oJ incub ation lo hatching

ONTOGENY OF EMBRYONIC BEHAVIOR IN AVES 249

,-

of two kinds of movements: (1) the bending and extension of thetru nk on the long axis of the body, an d (2) the twisting of thebody to the sides (in twisting the anterior region is bent to theopposite direction in which the posterior region is bent) (Kuo, I).Both kinds of t runk movement begin to diminish in frequency,magnitude aad in th e number of cases by the tent h day an d dis-nppcnr ant,ircly by t,hc t,wclfth d ny (table 4). With thc disnp-pearance of these two types of trunk movement, the jerking and

raise its head upon the neck, and so the head movement is trans-fornled illto lateral tur~ iing. (I t nus st be noted t11:~t ur i ~ ~ gticu-bation th e weight of the head in proportio~i o the total wi gh t ofthe embryo is decreased day after day while that both for the

TABLE 2Averaged weigh ts of head, neck and body of chick embryo s

' neck and for tho body is increased ( table 2).)Eflects of slructzcral changes on trunlc ntove??zenls. Trunk

movement appears by the fourth day of incubation. I t consists

-. . . --. nODYEMRRYOR WEICIRT

I T 1 I , 1 /Wcin l ~ t I'nr cot i t W e i a l ~ t Por cont Weight Per cont------ram8wriggling movements of t he body are increased in frequency andbecome the major or almost the only movements of t runk throughthe rest of the incubation period. I t must be pointed out th atalthough jerking and wriggling movements are observed even asearly as the fifth or sixth day of incubakion, they are rather minorand relatively infrequent responses of the trunk until after aboutthe tenth day.

Th e disappearance of the bending and extension and of theCOIIPARATIVE PBYCIIOI.OCiY, VOL. XIIT. NO. 2

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ZING YANG KUO O N T O G E N Y O F E M B R Y O N I C BEHAVIOR IN AVES 25 1T A B L E 3

Averaged tenglh of different parts of the body of the chick embryo

mm.

16.42 3 . 128.234 .939 .846 .253 .559 .968..575 .28 0 . 788 .898 .2

105.5113.7116.0118.5

TA BLE 4

lateral twisting of th e trunk is a necessary result of th e changesboth in structure and in the embryonic environment. In the firsthalf of incubation th e body is relatively light in weight and small

A O E OP E M D R Y O B

456789

1011121314

in size so that it floats, as i t were, on th e top of the yolk sac.There is th us sufficient space in th e egg for extensive trunk move-ments. But after the tenth day the embryo grows rapidly b othin size and in weight, its head is bent on th e breast permanently.After the eleventh day, it comes to lie with its dorsal surface incontact with th e egg shell, the ventral wall and left side (and asrnall part o f the right Ride) of t he body being covered by t heyolk sac (see Kuo, 11). I n such a position it is obviouslyimpossible for any extensive movement of the bod y and t he onlypossible mode of motion for the trunk is jerking, and wriggling(wriggling differs from jerking only in the degree of violence).

&fled of strucLural changes on limb movements. Active move-mcrlts of l)ot,h nntcrior nrid posterior limbs are observed on t heforit.I,1i th y of iricuI):~t,ion. As tlit: Iitril~s ire ~ h o r t nd rudirncn-tary, they a t first move in a vibrating fashion. But in the five-or six-day embryo, the limbs are longer so that they can movecephalad and cnudnd. Adducting and abducting movementsare also seen during these days. By the eighth or ninth day, themovement of t he forelimbs takes a new form. Now they ar emuch longer than the nntcrior limbs of the six- or seven-dayembryo; the main divisions are well defined, and they appeardecidedly wing-like. As a result of such str uctura l changes, theformer modes of motion of t he anterior limbs on the sixth an d' seventh d ay ar e now transformed int o flapping and slashing move-I ments. In these later movements, the wings can be extendedf~illy,icndward 3 r d tsilw:~rclns well as laterally. By the oighth5; day separ ate niovcnicnts of the arms, hand, arid digits, though1 not independent of the movements of other parts of the body, are

ri also seen.! Furthernlore, in the five- or six-day embryo, the forelimbs areI always straight both a t rest a nd in motion. But by the eighthor ninth d ay, due to lengtherling of the limbs and the appearance/ to their divisions, their movements consist chiefly of extensions6 and flexions.i After the ninth day, the forelimbs are further lengthened so1 th at t hey are held tightly against the body walls by t he environ-r mental conditions to be described below. Under such conditions1

T R U N K M O V E M E NT SNumber of e m b r y w

24 144044644644644622 1124

Frequency per minute

4 . 26.98 . 7

12.212 .811.26 . 82 . 2

Estimated magnitudemm.

1 . 93 . 13 . 33 . 23 . 83 . 63 . 02 . 2

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ZING P ANG KUO

the wings can not be extended laterally an d so the flapping move-ments practically disappear. Now the wings can only be ex-tended headward, upward, tailward or toward the breast. Whencolumes 8 and 9, table 3 , are examined the relation between thelengthening of both fore- and hindlimbs and the changes in themode of limb movements should be very obvious.

As to the rnovclncnts of t,lic iliritllilubs, tltc cfTccts of sLr.ucturn1changes are very much the same. In the four- to six-day embryothe modes of motion of t hc hindlirnbs are similar to those of theforelirnbs. At first thc posterior limb buds move also in a vibrat-ing fashion. By the fifth and sixth days of incubation, inwardand outward, and headward and tailward movements arc ob-served, the limbs always being straight. Aftcr the sixth day, themain divisions of the legs begin to become well defined. The legsare much lengthened. As a result, the legs are no longer in astraigh t condition; flexion and extension take the place of theheadward and tailward motions. The inward and outwardmovements also disappear for the amnion interferes with suchmovements after the legs are lengthened. With the appearanceof the divisions of the legs separate movements of the toes andshanks (but not independent of the movements of other part s oflegs) are also recorded.

On the eighth day, the legs are straightened in extension. Butfrom the ninth day on, the legs are further lengthened and beginto be folded on the breast so that they can not be fully extendeddtlc to thc obstruction of t,llc l~tritlio~ittld yolk s:tc or tllc cgg ~ltcllas th e case may be.

E N V I R O N M E N T A L EFFECTS O N E M B R Y O N I C B E H A V I OR

I Meaning of embryonic environment. The term "embryonicenvironment" is here used to refer t o those extra-embryonicfactors confined in the egg shell which exert influence on theI behavior of the bird embryo. They include the extra-embryonicmembranes, the shell rnembranks, the egg shell, the yolk, theI - -albumen, and the fluids in the extra-embryonic cavities. 'I'hemovements of certain part s of t he body which serve as stimuliIor movements of certain other body parts are also considered inthis report as cnviron~nr.ntalnctors i n bchnvior.

O N T O G E N Y O F E M B R Y O N I C B E H A V I O R IN AYE0 253Th e egect of yollc sac o n behavior

a. Th e eflects of the movem ent of the yolk sa c, and of the contrac-t ion o j the amnion . The yolk sac movement nnd amnion contrac-tion have been described in the first report of the series (Kuo, I) .

04 5 6 7 8 9 10 1 1 12 13 14AGE OF EMBRYOS (IN DAYS)

Here we wish to merely present some data concerning the relationbetween activities and t he movements of the yolk sac and amnion.Table 5 gives the average frequency per minute and magnitudeof the swinging movements and movements of the yolk sac and of

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254 ZING PANG KUOthe amnion for 328 chick embryos from the fourth to the four-teenth days of incubation. It will be clearly seen that the fre-quency an d magnitude for the passive swinging of thc embryoare in correspondence with those for yolk sac movements and

T A B L E 5Conlracl io7hq of n~ ~t tr i on ,olk ant: n~ovnntc~rlnnrl pnnnitrc .~ini?rgi~rgn, j thr: chic kembru o f r o m the fou r th dav to the Jourleenth dav of in c l i ba l ion

BWlNOINO 1 AMNION CONTRACTION YOLK SAC MOVEYPINT*on OF Fre- Eati- Number Fre- Eati- Number Frc- Esti- NumberEMBRYOE quency meted quency mated quency mate!l ofI .EtO?.I;-em.',m .Kte 1x- mp:b Iernbrym

P ~ - - - - . - -

TABLE 6Averaged frequency of loin2 body activities per minute of 598 chick embryos jrom thethird dni j o f incnbation lo hnlchinn

amnion contraction. This correlatiorl appears more striking infigure 1.Not only is thepamive swing effected by the yolk sac movementsand amnion contraction, but also the active movemerits of theembryo are increased or decreased according to the movements of

Frequencyof activi-ties .......

the amnion and of the yolk sac. Table 6 gives the average fre-quency of active body movements per minute for 328 embryosfro~nhe third day of incubation to hatching. Attention is calledto the fac t tha t in the chick embryo the body generally moves as a

6 7 e s t o t , 1213 lslsist7,crmsoAGE O F EMBRYOS (IN DAYS)

AO Q OF BMARTOA

whole (Kuo, V). The movements recorded in table 6 are alsomovements of such a nature. It will be noted tha t the number ofactivities is increased between the fifth and the tenth days ofincubation, especially between the seventh and ninth days, thatis, dur ing the period of forceful amnion contractions and yolk

a 2021

1 . 34 . 36 . 28 . 812 . 112 . 411 . 96 . 12 . 33 . 12 . 23 . 33 . 32 . 93 . 12 . 82 . 93 . 5

9 13oa 7 14 15 16 197 is

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256 ZING YANG KUOsac movements. If we plot curves for the frequency of theamnion contraction and yolk sac movements and for the fre-quency of activi ty during incubation, again we find the two curvesrunning almost parallel (fig. 2). In observation we find that themovements of the amnion and of t he yolk sac not only s ta rt thepassive swinging of the embryo, bu t also stimulate active move-ments of the wliole body. Indeed, during the pcriotl of activeamnion contraction (and yolk sac movements) body movementsare almost ceaseless. As thc frcqucncy and mag~ iitu dcf amnioncontraction begin to decline, the embryo becomes less active.

b . Leg movenzents. We have stated tha t from about the ninthday on, due to the irlcrcasc in length, the legs begin to bc foldedciow~i n the brcnsl,1)y tIlo :urit~iori. Ilrrf,:~fI,t:r al)ollI, I,hc t~lcvcrrt,hday, the yolk sac is ge~iersllymoved over the ventral side of theembryo (Kuo, 11) so th at the legs are directly under th e yolk sac.Under these conditions the extent and frequency of leg movementsare reduced; the more the yolk sac is pushed over them, the moredifficult i t is for the legs to be extended. Under the yolk sac, thelegs, in their upward and tailward cxtensiotl have to push up theamnion and the yolk sac. Sometimes the latter may be pushedup from 4 to 6 mm. Bu t the weight of the yolk and yolk sacpresses the legs down to fold on the breast again. In the secondarticle of this series we have pointed ou t th at during the latterhalf of incubation as the legs are too strong to be k ept in properconfiguration by the amnion alone, the yolk sac is chiefly respon-sible for pressing down the legs on the brcast. Thus in thoseabnormal cases in which the yolk sac fails to come over the ventralside, the legs may be extended as far as the shell, or fully extendedand twisted in any direction. In such cascs, the legs generallyacquire an abnormal configuration.Between the eleventh and t he fourteenth days, after the legs arefoldtd under the yolk sac, a new mode of leg movements appearswhich is much more extensive and frequent than the upwardextension. This is the forward thrusting of th e legs. In the for-ward thrusting movement, the legs are extended cephalxd. Theymay be extended over tlie beak, the head, or toward the neck atany level of the cervical vertebrae (sometimes both legs are

ONTOGENY OF EMBRYONIC BEHAVIOR IN AVES 257thrus ted to one side of the neck) or in fr ont of the lower jaw orthe vent ral aspect of the neck. I n such movements the legs maybe extended as far as 10 or 12mm. Th e forward thrusting move-ment of the legs is most frequent and extensive by the twelfth d ayof incubation. Bu t both extent and frequency are reduced almostby half by the end of the thir teenth day. The y are furt her re-duccd by t he fourteenth day. By the th irteenth or fourtcerlth daythe legs in thrusting can not be extended much below the eye level.Aftser the embryo turns so as to lie lengthwise of the egg, thegreater part of the yolk sac is pulled over on the legs which arefolded on the breast. The yolk by the eighteenth day of incuba-tion still weighs several grams. Wit h such a heavy yolk pressingdown o n t,hc I ( : ~ R , it is nnt11rn.l thnt they nrc forccd to rcmnin in nfolded position throughout the rest of incubation. In this posi-tion, not only the upward extension bu t also the forward thrust ingof the legs are reduced to a minimum. In most cases, after theturning of t he body, t he legs can not be observed. But in a fewchicks, the legs are seen to perform only very slight movementstogether with the scratching motion of the toes.In the second article of this series we have reported the fac t th atif the yolk sac does not come over to cover the ventral side of thebody and the legs between the twelfth and fourteenth days, thebody of t he embryo can not be turned to lie lengthwise of the egg,as the turn ing of the body very much depends upon the movementof the legs to push t he yolk sac upward so tha t the body under theyolk snc can slip townrd the small end. I t need not be mentionedthat if the legs at thi s stage are still under the shell instead ofbeing under the yolk sac, their upward extension is impeded bythe shell.In the second article we also reported th at in the at tempt on thepar t of the hatching chick to gain egress from the shell, the move-merits of t he legs played an important rBle, but t ha t such move-ments are no t effective until after the yolk sac covering the legsis drawn into the body cavity.In the fifth article we shall describe how the progressive move-ments of the legs are acquired after the yolk sac has been pushedto cover the legs.

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258 ZING YANG KUO ONTOUENY OF EMBRYONIC BEHAVIOR IN AVER 259c. Win g movements. We have shown tha t as a result of length-

ening of the wings and of environmental conditions, flappingmovements disappcar, and a new mode of movement takes itsplace (extension headward or toward the breast). Here both theamnion and yolk sac play their part. In the later period ofincubation, the wings are held tightly against the body walls byby the amnion. Aftcr tjllc tcntll dny thc body of the cmbryo isgenerally so fixated that the yolk sac presses from the left, thechorio-allantois and the inrier shell membranes next to the air cellpress from the right. By about the fourteenth day a small por-tion of the yolk sac is pushed over the ventral wall to cover a smallpart of the right side of the body, including a large portion of theright wing. The flsppilig movements of the wings are thus inter-fered with, and the wings now can only be drawn up and downlightly against the body walls. When the wing is drawn up itmay be extended cephalad or toward the breast. This mode ofwing movement remains throughout the rest of incubation.

d. Head movements. We have already shown that due toanatomical changes, head lifting is transformed into side turningbetween the fifth and tenth days of incubation. Now after thetenth day the proportional size and weight of the head is not solarge and heavy as before and it would seem possible to reinstatethe head lifting movement. But this is not the case owing to thefact that between the tenth and twelfth days, the body whoseanterior and posterior ends are bent toward the middle regionsinks into the yolk sac so that t he dorsal side of the neck and ofthe body is in direct contact with the yolk sac while the headwhich is bent on the breast is very close to the shell. In thisposition the raising up of the head upon tlic neck is diiiicultalthough lifting of the beak has been frequently observed. Afterthe twelfth day a portion of the yolk sac has come over, as hasbeen repeatedly stated, to cover the ventral wnll as well ns thebeak and the head, while the dorsal side of the neck is now in i!direct contact with the shell. Here again, head lifting is prac- itically impossible. This condition persists until the yolk sac in ithe large end of the egghas been withdrawn which generally takes tplace between the eighteenth and nineteenth days. But even I

after the withdrawal of the yolk sac from the large end, head lift-ing is still extremely difficult as the neck has now acquired adouble bend. However, slight lifting and forward thrusting ofthe beak are frequently observed during this stage, and thesemovements are responsible for the piercing of the membranes(Kuo, XI).

In a word, structural, positionnl and environmental conditionshave caused a permanent disa.ppearance of the head lifting move-ment af ter about the fifth day of incubation.

T A B L E 7Average frequency of right and lef t turning of the head in hirty minu tes i n 344 chickembryos

The yolk sac Ilas also a, great effect on the laternl turning of thehead. As a result of torsion, the embryo comes to lie with its leftside on the yolk. After the fourth da.y of incubation the embryosinks down into the yolk sac so that in normal cases it lie8 with itsback on the yolk sac while the left side of the body and of the head .is in direct contact with the yolk sac. In th is position the turn-ing of t,he head becomes almost unilateral, t ha t is, the head tendsto turn away from the yolk sac, in other words, it tends t o tu rn tothe right rather than to the left. This tendency is especially

LEFT TURNINO

2371606140ao121246363000

AOE OF EMBRYO

45678910111213141516171819

RIOnT TURNING

3010017028135031614213784869382871.51021

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260 ZING YANG KUO ONTOGENP O F EMBRYONIC BEHAVIOR IN AVES 261strong after the stage of fixation of position (Kuo, 11). Table 7shows the relative frequency of turning of the head to the left andto the right between the fourth and nineteenth days of incubation.It will be seen th at during practically every day of incnhatian_

minimum. Not only the movements of the head and extremitiesand extension and lateral twisting of the t runk are impossible,but also jerking and wriggling movements are rarely observed.On the other hand, wriggling af ter the eleventh day and through-out the rest of incubation takes place only when the vent ral wallis under th e yolk sac. We have described the processes of t urn-ing of the body to lie lengthwise of the egg and of the protrusionof the neck into the air cell (Kuo, 11). These are accomplished bywriggling movements which are always performed under the yolksac. Thus, we have found tha t if the yolk sac does not come overto properly cover the ventral wall and the legs after the four-teenth day (tha t is, if the yolk sac is still under the back, or oneor both lcgg are not covered by the yolk sac, or the whole yolksac is behind the left of the embryo (Kuo, 11)) not only does thebody fail to turn to lie parallel to the long axis of the egg, but alsowriggling movements are greatly reduced both in frequency andstrength.

g. Turning to the body. In the second article we reported thatwhen the embryo began .to turn to lie lengthwise of t he egg, th eturning movement was always caudal, that is, the tail end wasshifted leftward toward the small end of th e egg. This was foundto be due to the fact tha t a t this stage, the neck of the embryo wasbetween the yolk sac (left) and the chorio-allantoise and innershell membranes next to the air cell so that the neck was held inplace during the turning of the body.

/.

l'he effect f Ihe membranes

right turning is by far more frequent than left It mustbe noted nlso that in prncticallv every rasp rgh agreater magnitude tllnn lcft turning.

a. Amnion. We have already shown that amnion contractionserves as a stimulus for active bodily movements. Th e period offrequent and powerful amnion contraction is also the period offrequent and violent body movements. When one observes forseveral minutes a six- to nine-day chick embryo, one can no t fail t osee that whenever the amnion contracts or the yolk sac moves,the embryo is set in both passive swinging and active massivemovement. During these days one frequently observes th at whenthe amnion contraction ceases, the embryo also rests quietly.(Body movement may also in tur n stimulate amnion contractions.)

It is very probable th at such an unilateral turning of the headhelps it to acquire the position, namely, the bending of the headtoward the right, which position is a prerequisite to hatching(Kuo, 11). In most cases of the bird embryo which we have ob-served, bending of the head t o the right has become almost afixed posture in the lntcr stnge of incubntion.e . Beak moventent. In the first report we have shown that thebeak can open and close by the seventh day. Now after the yolksac has been pushed over to cover the ventral wall and the beakwhich is bent on the breast, beak opening is reduced both in fre-quency and magnitude. In this position, the head sometimesturns o ut from the yolk sac, making it and the beak free from theyolk sac. The beak is then often observed to open widely. Butwhen it is turned in under the yolk sac again, bill opening is alsodiminished. However, when the beak is under the yolk sac, itacquires a new mode of motion, namely, the clapping of the bill.In clapping the beak is only very slightly opened. It claps fre-quently; the embryo is often observed to clap its beak every fewseconds, nnd mnkes severnl clnppings consecutively.j. Trunk movements. The effects on t runk movements of theyolk sac has already been pointed out. When the body grows insize and weight, it sinks down into the yolk sac so as to lie with itsback and left side in contact with the yolk sac. The extensionand lateral twisting of the body is thus impeded by the yolk sac,and so. the trunk movements are transformed into jerking andwriggling, a s has been previously stated.

Before the eleventh day wriggling is possible only when theembryo lies with its dorsal side on the yolk sac. In youngerembryos, if the body lies under the yolk and the yolk sac, it is sopressed by the latter that bodily movements are reduced to a

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262 ZING YANG KU Ob. Th e chorio-allantois and the inn er shell membrane. As far as

behavior is concerned, only tha t part of the chorio-allantois andinner shell membrane which separates the air-chamber from therest of egg is important. We have already referred to the factth at during the turning of the body to lie lengthwise of the egg,this part of the mexn1)rnne keeps the neck from moving. Thus,ns rcl)orlcd in tlic scco~ld u.Liclc, tlr~r it~gl~is Lrigo, f t,llc ~nclri-branes are too loose or are punctured to allow air to run in, thebody may immediately fall to the left or turn so as to acquire anabnormal position.

The protrusion of the neck forward and downward into theair-chamber under the membranes (Kuo, 11) depends on thewriggling movcment,~. Now, if during this stage, thc mem-branes are lightly applied on the left side of the head and neck,wriggling as well as movements of the head, beak and the rightwing are reduced to a minimum and the embryo generally fails topass this stage. Under this condition, lifting and forward thrust-ing of the beak are rarely observed. Beak opening is also infre-quent, and the only relatively frequent motions observed areeyelid movements and bill clappings. On the other hand, if,before and after the protrusion of neck, the membranes are loose,all above mentioned movements a re increased.

The eflect of position on behaviora. Position of the h,ead. In the later period of incubation, the

hcn.d is gcncrally bent on tlic brcnst, t11c forchcnd bcirig under thcyolk sac. In this position the head o~l lyurns to the side. Thebeak may be able to lift up a little but the head can not raise uponthe neck. After the yolk sac has been drawn into the body cavity,raising of the head is also extremely difficult as its dorsal side israther close to the shell.

After the protrusion of the neck the double bending of the neckis rather pronounced (that is, the neck is bent on the breast, whiIethe head turns away from it so tha t the right face faces the mem-branes (see Kuo, 11)). In this position, the head can neither liftup nor turn to side, and no other movements than upward lifting,opening and slight forward thrusting of the beak are observed.

ONTOQENY OF EMBRYONIC BEHAVIOR IN AVES 263Bu t if the head is too close to the shell, or still bent on the breast,or tilted to the left or right, or is in the small end of the egg, anymovement of the head and the beak (except bill clapping) becomesimpossible, as there is no room for movements.

After the protrusion of the neck, if the head is tucked under theright wing, bill movements are increased both in frequency andnrtiplit,udc. OLIicrwi~e,licy nrc diminished (Kuo, 11).b. P ositio ns of the win gs and legs. The effect on behavior of thepositions of the wings and legs has been discussed in previous sec-tions. It remains to be state d that if, in the later period of incu-bation, the legs are not folded on the breast under the yolk sac,the normal leg movements previously described are not observedand coordi~~atcd alking movements (ICuo, V) can not beacquired.Th e efe ct of the beating of the heart and of the scratching of the toeson head movements

a. The beatiG . the early stage of developmentr e m o he thorax (generally about theeighth day of incubation) its movement often serves as a stirnula,tion for head movements. In the first article of this series wehave already described the passive vibrating movements of thehead and the body which are produced by the beating of the heart.\In the four- to sevenda v embrvo the head is bent down close to 1the heart so th at cardiac movements often touch the head. Thehcnd i~ then stimul:~ted,nnd motion i~ observed, that i ~ ,he headturns away from the source of stimulation, namely, the heart.The turning of the head away from the heart results in the liftingof the head, or turning to the side, as the cnse may be. Such headmovements are almost always accompanied by massive move-ments of the body. In fact, from continuous observations onmany hundreds of chick embryos between fourth and ninethdays of incubation we have come to the conclusion that the factthat the activity curve of the embryo reaches its highest peak inthis stage is to be explained by the fact that in this stnge thecontraction of the amnion, the movement of yolk sac and thepassive swinging of the embryo as well as the beating of the heartp

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264 ZING PANG KUOall serve as external stimuli for active movements of the embryo.I n th e sixth article we shall present evidences to show tha t th erat e of hear t beat is also highest when th e embryo is most active.On the other hand, in the later half of incubation, the heart isenclosed in the thorax, amnion contraction, yolk sac movementnnd pnssive swinging are either greatly reduced in frequency andin xrlng~~ituder cclisc nltogctlicr, r~rid he body grcatly ilicl.cnscsin size so that extensive movements are not permitted by theexternal cnvironmcnt; nnd so the ernbryo becomes rather quiet;it may be motionless for many minutes, and when it moves occa-sionally, its movements are no t extensive.b. The moventent of the toes. By about the fourteenth day thebody of the embryo which origirlally is at right angles to thc longaxis of the egg, turns to lie lengthwise of the egg. As a result, thehead is bent away from the breast with the right face turned for-ward toward the membranes next to the air cell (for details seeKuo, 11). In th is position, th e toes of both legs are just behindthe left side of the head. Now it often happens th at when thetoes move, they scratch the left side of the head. This stimulatesthe head which turns out toward the membranes. (In this stagethe head and the beak is generally under the yolk sac so tha t inturning out toward the membranes, the head is temporarilyremoved from the yolk sac.) This is another reason why thehead, after the turning of t he body, makes so few turnings to th eleft (tabIe 7).m SUMMARY

& I n this paper data are presented to show that structuraland environmental changes are always accompanied by behavioralchanges in th e embryonic chick.3. s a result of the enormous increase in the size of the head,

head lifting is transformed into side turning.3. Bending and extension and lateral twisting of the t runk dis-appear and jerking and wriggling come to take their place whenthe size of the embryo is increased.

4. The modes of movements of both the anterior and posteriorlimbs are partly determined by the length and sha.pe of the limbsn t cncli stngc?of dcvcloprnc~~t..

ONTOGENY OF EMBRYONIC BEHAVIOR IN AVES 2655. The contraction of the amnion and the movement of the

yolk sac all serve to stimulate m0vement.s of the bird embryo sothat the period of greatest amnion contraction is also the period ofgreatest behavioral activity in the embryo.

6. The mode of leg movements is also determined by it s posi-tional rclation with the yolk sac.

7. Movcrncnt~f othcr pa rts of tlic body nrc nlso partly cffectcdby their positional relation with the yolk sac.8. The movements of t he toes and the contraction of the heart,the positions of the hcnd, neck and the legs and the extra-embry-onic membranes all play their part in determining embryonicbehavior.

DISCUSSIONEnough facts have been presented to demonstrate that changes

in gross anatomy and environment are important factors indetermining embryonic behavior in birds. We are firmly con-vinced that in the study of the development of behavior thesetwo factors ,as well as the effect of past behavior and the develop-ment of the physiology of different organs must be taken into con-sideration. It is regrettable that recent investigators on em-bryonic and fetal behavior in amphibians and mammals do notgo beyond the mere noting of the appearance of certain move-ments. They make no attemp t whatever to find out the causalfactors for such movements. The historical, anatomical, physio-logical and environmental factors are all ignored, and the appear-ance of movements is described as "spontaneous a~ ti vi ti es ." ~

One has only to observe a chick embryo for several days t o bereasonably convinced th at external (i.e., extra-embryonic) stimuliplay a very important part in determining embryonic behaviorand that embryonic activities are rarely spontaneous. In fact, inthe caye 01 the avian embryo, food and oxygen supply is relatively

Some writers , e.g. (Trac y (X926)), h a v e a t t a c h e d a n e w me a n in g t o t h e t e r m" sp o nt an e ou s, " t h a t i s t o s ay , w h en c e r t a i n mo ~ e m e n t ~ sre os tens ib ly caused byi n t ernal s t imul i wi th in the o rgan ism, th ey are refer red to a s " spontaneous act iv i -t ies ." But even so , i t can no t escape the cr i ti c i sm tha t " spontaneous act iv i ty"is nothinu more thnn n nnrnc for our ignora nce of the t-tctual physiological fa cto rsu11 t l c r l y i 1 1 ~) c l ~n v i o r .

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266 ZING YANG KUOconstan t and movements activated by lack of metabolic materialsare ra ther rare exceptions.

Th e neglect of environmental factors in embryonic life has ledmany writers to believe that prenatal movements are innate orhereditary. Th at this is not the case has been clearly demon-strated by our observations on the behavior of the bird cmbryo.We shnll discuss rnorc fully thc qucstion of licrcdity in rcl: t' 011to embryonic behavior in th e fourth article of this series and espe-cially in a book cnti tlcd "The Mccha.nics of Embryonic Behaviorin Birds."

Suffice it to point out here that practically every prenatal move-ment is shaped and determined in part, a t least, by the nat ure ofthe embryonic environment.

The importance of analysis of environmental factors in behaviorstudy can not be overstressed. Every movement is caused by

A some environmental stimulation intra-organic or extra-organic.-There is no such a thing as "spontaneous actiwily," any more tha nis there such a thing as "spontaneous generation." To understand\ the nature of the environlnent and hiw it shapes and determincsbehavior is the key to the understanding of the causal relation ofanimal activities. Too many behavior studies, especially thosedealing with prena tal behavior or behavior of the newborn, havebeen carried out with environmental factors either entirely neg-lected or trea ted only in a casual manner.

The importance of nnatomica.1 and physiological factors inembryonic bcllravior I I : ~ dso )c:oll ovcrlooltcct. 'I'll(: trr~.tlitioncalview th at the development of the nervous system alone is corre-lated with the devclopmcnt of bchavior is partly responsible forsuch a neglect. Recent studies by Coghill and others otl tIiccorrelation between the development of the nervous system anddevelopment of behavior chiefly in amblystoma, and cats andrat s have been carried out without reference whatever to thechanges in the environment, in gross anatomy2 and in the physi-ology of various organs. Th e effect of previous reaction on latermovements has also not been taken into consideration. While it

* The workers on mammalian fetal behavior have not gone beyond the meremeasurement of body length of fetuses under observation.

ONTOGENY OF EMBRYONIC BEHAVIOR IN AVES 267is not our intention to minimize the importance of the nervoussystem in connection with the development of behavior, we wishto express our doubt concerning the view that morphologicaldevelopment of th e nervous system can be used as the absoluteindex of behavioral development.

The prepared scctions of the nervous system of the amblystomaby Cogl~il l rc, of coursc, objcctivc. n u t mnny of his inte rpreta-tions are open to objections. In the fifth article of thi s series weshall point ou t tha t his explanations of dominance of t ru nkmovements over the gill movement are far-fetched. We wish togive here another instance to show th at Coghill's views are farfrom being adequate.

Coghill believes tha t the development of behavior is solelydetermined by the growth of th e nervous system. He says:"Growth of the terminals of axones and dendrites through microscopicdimensions is sufficient to have profound effect in behavior. This wehave demonstrated in the first lecture in a vertebrate of such primitiveform as Amblystoma, which, by the growth of the terminal of nerve cellsover a distancc of less than one one-hundredth of a millimeter, trans-forms itself from an animal that must lie helpless where chance places itinto one that can explore its environment in response to impulses fromwithin or stimulation from without. This is for amblystoma a discovery,so to speak, of incalculable significance. It is to all intents and purposesa solution of one of the crucial problems of life" (1929, pp. 84-85).

Tf t,l~ist~t~cr.prcl;ntronf Coghill i~ corrcct, indccd, if th e meregrowth of 0.01 Inm. of t he terminal of nerve cells is really respon-sible for the capacity of the amblystoma larva to swim, this 0.01mm. of ncrvc ter~n innlsmust be nothing short of a miracle. Bu thas Coghill taken into account other morphological, physiologicaland even environmental changes which have taken place beforethe amblystoma can swim? During this stage, are there notchanges in the amblystoma in general metabolism, and in themorphology and physiology of the muscular system? Do thesechanges effect the swimming movement of the amblystoma? Inthis paper we have presented enough evidence to show tha t suchchanges are at least just as important as the morphological

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ZING YANG KUO

changes in the nervous system. And yet in Coghill's work suchimpor tant factors are entirely ignored.

To make my point clear, I will cite one simple experiment on thechick embryo. One or two days before hatching, the entire shelland both the outer and inner shell membranes are removed (in

branes, too, are not sufficiently dry until the moment of hatching.All these tend to impede the movement of the chick. In otherwords, it is the environmental changes, such as the enclosure of

some cases a small portion of the chorio-allnntoic membrane isnlso pierced to ndt i~i t~iror brcntliilig) so t~ so c~ l low he clliclc toget out earlier than the control ones whose egg shell and shellmembranes are intact. But , contrary to our expectation, theseexperimental chicks do not atte mpt t o get ou t any sooner than thecontrol ones (not even half an hour earlier); they lie motionlessand much more helpless than Coghill's amblystoma before theIntter cnn swim. And t,llcrc is not tho slightest nt,tcmpt on the partof tlic exycrimc~ital hick to "explore its environrncnt" bcfore thetime when the control chicks attempt to gain egress from theshell. Is this failure on the part of the experimental chick to solveits "crucial problem of life"# sooner than the control ones due tothe fact that 0.01 mm. of nerve terminal has not arrived to per-form the miracle? Of course, no one denies the possibility ofmorpho1ogica.l growth of the nervous system during the intervalbetween the operation and the time of hatching. But that sucha growth of nerve cells is solely responsible for the ability of thechick to hatch is, a t least, very questionable. A much simpler

Indeed , if one i s t e l eolog ical -minded enough , one should th ink th at the p rob-le m is by far more crucia l fo r the hatch ing ch ick than fo r the am blys toma Inrva .

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ONTOGENY OF EMBRYONIC BEHAVIOR IN AVES 269

bu t more correct explanation of the case is this: The hatchingchick must have gained sufficient muscular vigor before it canemerge from tllc ~llell. This cnn only i>cgnincd nitor long l~oarsof pulmonary respiration which takes the place of chorio-allantoicrespiration one or two d ~ y scfore hatching. Thus, many chickshave died before hatching as a result of the faTlure to e s t a b mp Besides, before hatching, there is still a

the yolk sac into body cavity, etc. (see Kuo, 11),and espe-cially, changes in' respiratory metabolism th at account for theabi lity of the chick to "solve one of the crucial problems of life."It is very doubtful that the growth of nerve terminals plays animpor tant part in such cases; for the movements by means ofwhich the chick gains egress from the shell are the very movementswhicli hnvc bccn in cxistcncc rnorc than tcri days bcforc hr~tching.4In other words, no new movements which would come about as apossible result of the growth of the nervous system are requiredfor the chick to be a.ble to emerge from the shell.

Coghill goes even so far as to assert th at "the normal experi-ence of thc animal with reference to the outside world appears tohn.vo noU~ingo (lo with t h o dctcrminntion of thc form into whichthc bcllnvior of tlie allinin1 is cast" (1'320, p. 87). One h,?a onlyto consider the evidences presented in this paper as well as in thefourth and fifth articles in order to be reasonably convinced thatCoghill's view is erroneous and wholly inadequate. Certainly thedevelopment of behavior, in higher vertebrates a t least, is too com-plex and complicated to be explained solely or even mainly byanatomical growth of the nervous system.

considerable amount of yolk sac over the folded legs and theventral wall. The liquid content and the extra-embryonic mem-

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i i i , N o . 4.RICHAT,X.: Allgemeine anato mic angewa ndt nuf die Physiologic und Arzneiwis-senschnf t . uber V. Pfnff. Lcipzig, 1803.BOLAFFLO,l. , A N D ARTOM , .: Ricerche sulln fis iologia del s istemn nervo sa delfeto umnno. Arch. d. Scienze biol., 1924, v, 457.BROWN, . T. : On the natu re of the fundamental ac t iv i ty o f the nervous cen ters ,togeth cr with nn nndysis of the condit ioning act ivi ty in progression anda theory of the evolution of function in the nervous uystcm. Jour.Physiol., 1914, xlviii, 18.BRO W N ,G . T.: On the act iv i t i es of the c en t ra l nervous sys tem of the unbornfoetus of the c nt with n discussion of th e quest ion whether progressionis a " learnt" reflex. Jour. Physiol., 1915, xlix, 208.

! he on ly d i fferencel ies in th e fac t tha t these movements a t h a t c h in g a r e mu c hmore vigorous than before the establishment of pulmonary respirat ion.

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if' 270 ZING PANG KUO

COQHILL, . E.: Correlated anatom ical and physiological s tudies of th e growth ofthe nervous sys t em in amphib ia . 111. T h e Floor Plat e of A mbly-stoma. Jour. Com p. Neurol ., 1924, xxxvii , 37-69.C o o r r ~ ~ r , ,. E.: Thc g rowth o f funct ional ncurones and i t s re l a t ion t o th e devel -opment of behavior. I'roc. Am er. I'hil. Soc ., 1926, Ixv, 51-55.C O G I ~ I L L ,. E.: Corre l a t ed anatomical , e t c . V. The g rowth o f t he pa t t e rn o fmoto r mechanism of Amblystoma puncta tum. Jour. Comp. Neurol .,1926a, X I, 71.C o a r r r ~ ~ ,. E.: Corrr ln t cd nnn to rn i rn l , r t c . VJ . T h e m r r h n n ia m of i n t c ~ r n t i o nin Amblystoma puncta tum. Jou r. Comp . Neurol ., 1920h, xl , No. 1.COOHILL, . E.: Anatom y nnd th e Problem of Behavior. Cambridge Univers i tyPress, 1929.COQEILL, . E.: Corre l a t ed anatomical , e t e . IX. The mechan i sm of as socia t ionof Amblystom a punc tatum . Jour. Comp . Neurol ., 1930, l i , No. 2.Icuo , Z.Y. : Ontogeny of em l~r yon ic ehavior of nves. I. The chrono logy and~c ne rn l rnturr of t l lc 1,rhnvior of t l rr clriclc rrnl ~ryo . (T o npl)cnr in. lo t~ r . 1 :~ l ) t . ool .)Icuo , Z. Y.: Ontogeny of einbryonie behnvior in nves. 11. Thc mcchnn ica lfac to rs i n the va r ious s t ages l ead ing to ha tch ing. ( T o a p p e a r i n J o u r .Exp t . Zool .)K u o , Z . Y.: Ontogeny of cmhryonie behavior in aves. IV. The in f luence o fprenatal behavior upon postnatal l i fe. ( T o a p p e a r i n t h i s J O U R N A L . )K u o , Z . Y .: Ontogeny of embryonic behavior in aves. V. The reflex concept inth e l ight of th e behavior of th e avnin embryo . (To a ppear in Psycho l .Rev.)Icuo , Z . Y.: Ontogeny of embryonic behavior in aves. VII. Expe rime ntal con-trol of embryonic posi t ions. (To appear soon.)K u o , Z . Y.: (a) Th e effects of malpo si t ions on the morphological development int h e b i rd e m l ~ r y o . (?o app ear in Ana t . Ree.)Icuo, Z. Y .: (b ) Causes and p reven t ion o f embryon ic mor ta l i t y in th e fowl. (T Oappear soon .)K u o , Z . Y .: (c) T he mechanics of embryon ic behavior in birds. (To be pu1,l ishedsoon.)L A N ~ ~ O R T I I Y ,. 12.: A rnrr clr~ tcd t~l dy f thc clcvcloprnrnt of roflcu nct ivi ty infe t a l and young k i t t ens and the myel in i za t ion o f t rac t s i n the nervous~ y ~ t e m .ontri l )rl t ion to Em bryo lom , 1929, xx, 127.MINKOWSKI, .: ub er Uewegi~rlgen nd Iteflcx des menechlicben foo tus wallrendder ers t en H al f t e sen ier En lwick lung Schweig . Arch fur neurol . undPsychiate., 1921, viii, 148.M ~ N K O W S K I ,I.: ub er f ruhse i t i ge Ben~egungen , Refl ex and musku lare Reak-t ionen beim menschlichen fotus und muskelcsystem. Schweiz. Mcd.Woc henschr ift, 1922, 721 an d 725.MI N K O W S K I , I. : Zur En twick lungs gesch ich te , Lokal i za t ion and Kl in ik desFussonleureflexes. Schweizer Arehiv fi i r Neurol . U. Psychiat., 1923,xiii, 475-514.MINKO WSKI, .: Zum gegenwiirt igen St and der Leh re von den Reflexen. U. S.W., ibid., 1924, xv, 239-259.

Z U N T Z ,N.: ub er d i e Resp i ra t ion des Saugeth ier foetus . Pfluger's Archiv. f. d.Ges. Ph ysiol., 1877, xiv, 605.

ONTOGENY OF EMBRYONIC BEHAVIOR IN AVES 271MINKOWSKI, .: Zum gegenwiirt igen Stan d der IJehre von den Reflexen. Neuro-log. U. Psyc hiats . Abhan dlungen (Fu ssl i , Zurich) He ft , 1925, i .PANKRATZ,. S.: Th e possible relat ions of the development of the supraren alg land to the o r ig in of t h e foe ta l movement s in a lb ino ra t . Aunt . Rec.,1930, xliii, 235.PATON,. : Th e reac t ion o f t he ver t eb ra t e em bryo to s t imula t ion and the nsso-c i a t ed changes in the nervous sys t em. RIitteiI. a. d. 2001. Sta te. Z.Neape l., 1907, xviii, 535.I'REYER,.: Spccicl l e J'hy~ io log ie l c ~ ml j ryo . T,eipzipl, 1885.S W E N S O N , . A . : The s imple movement s of t h e t run k of t h e a lb ino-ra t fe tus .An at . Rec., 1928, xxxvii i, 31.S R E N S O N , . A ,: Motion pictures of ac t ivi t ies of l iving albino-rat , fetuses. Anat .Ree., 1928, xxxviii, 63.S W E N S O N ,. A.: The ac t ive s imple movement s of t he a lb ino-ra t fe tus . Anat .Rcc., 1929, x l i i , 40.T n h c : ~ , 1. C.: 'I'll(: t l r v r l o ~ ) ~ r ~ r r i f ,f tnoti l it ,y n.nt l I~nhnvior rn ct i on ~r i l,lrr tondfish( O ~ " ! I . ~ I I Srui). .lour. Corn!). Ncrlrol., 1920, X I, 253.W I N D L E ,W . F.: The ear l i es t fe t a l movement s in the ea t co r re ln t ed wi th theneurofibri l lar development of the spinal cord. Anat . Rec., 1930, xlv,249.