ORI GIN AL PA PER

Seeking the constant in what is transient: Karl Ernstvon Baer’s vision of organic formation

Florence Vienne

Received: 8 July 2014 / Accepted: 16 November 2014 / Published online: 7 January 2015

� Springer International Publishing AG 2015

Abstract A well-established narrative in the history of science has it that the

years around 1800 saw the end of a purely descriptive, classificatory and static

natural history. The emergence of a temporal understanding of nature and the

new developmental-history approach, it is thought, permitted the formation of

modern biology. This paper questions that historical narrative by closely ana-

lysing the concepts of development, history and time set out in Karl Ernst von

Baer’s study of the mammalian egg (1827). I show that Baer’s research on

embryogenesis aimed not simply to explain temporal changes, but to inscribe the

formation of new individual organisms into a continuous, unending organic

process. I confront Baer’s views with other explanations of embryogenesis

arising in the 1820s and 1830s, especially those of Jean-Baptiste Dumas and

Jean-Louis Prevost and of Theodor Schwann. By highlighting divergences

between these scientists, especially as to their view of the role of gender dif-

ferences in reproduction, I argue that biology evolved not from a homogeneous

concept of developmental history but out of various, even opposing, views and

research programmes. Thus, the birth of biology did not imply the end of all

natural history’s thought models.

Keywords Developmental history � Embryology � Cell theory � Reproduction

In the late eighteenth century, a new configuration was to appear that would definitively

blur the old space of natural history for modern eyes.

Michel Foucault, The Order of Things, 162

F. Vienne (&)

Abteilung fur Geschichte der Naturwissenschaften mit Schwerpunkt Pharmaziegeschichte,

Beethovenstr. 55, 38106 Braunschweig, Germany

e-mail: vienne.florence@berlin.de

123

HPLS (2015) 37(1):34–49

DOI 10.1007/s40656-014-0057-3

1 Introduction

To mark the opening of Konigsberg’s zoological museum in 1821, Karl Ernst von

Baer (1792–1876) gave a speech on the ‘‘current state of natural history.’’1 Baer

painted a rather disparaging portrait of natural history: the field, he complained,

remained too narrowly restricted to merely collecting, observing, describing and

classifying. What was there to be learnt by introducing more and more new species,

continually renaming them, and multiplying the names for a single object? The fact

that the number of mammals described in zoological works had trebled since

Linnaeus’s day was just one of the many examples Baer offered to send his

audience’s heads spinning and demonstrate the absurdity of a purely quantitative

proliferation of ‘‘catalogues’’ (von Baer 1821, p. 31). Baer’s words reflect the

enlargement of experience and knowledge in this period that has been described by

Wolf Lepenies (Lepenies 1976, p. 21). According to Lepenies, a constantly

accelerating quantitative expansion of knowledge in the last third of the eighteenth

century thrust natural history—with its descriptive, classificatory and spatial

orientation—into crisis, prompting the adoption of ways of thinking based on

history and, more narrowly, developmental history (Lepenies 1976, p. 45, 16). It

was this process of ‘‘temporalization’’ that, in Lepenies’s view, helped to overcome

the crisis, yet also brought about the ‘‘end of natural history’’ itself (Lepenies 1976,

p. 24). A decade earlier, in The Order of Things, Michel Foucault had portrayed the

transition from natural history to the history of nature in no less dramatic terms:

‘‘One day, towards the end of the eighteenth century, Cuvier was to topple the glass

jars of the Museum [of Natural History], smash them open and dissect all the forms

of animal visibility that the Classical age had preserved in them’’ (Foucault 1974,

pp. 137–138). In Foucault’s account, Cuvier’s gesture stands for ‘‘the end of

history’’ as it was understood by the likes of Linnaeus or Buffon, and the beginning

of an epoch in which a history of the living became thinkable (Foucault 1974,

p. 138, see also 263–279). This historiographical image, shaped by Foucault and

Lepenies, of the transition from a spatial and static ‘‘natural history’’ to a historical

‘‘biology’’ is what the present essay will critically address, starting from the work of

Baer.2 Only a few years after Baer formulated his criticism of natural history, he

published groundbreaking new studies in embryology and developmental history.

The case of Baer is therefore a fruitful one through which to examine the early

nineteenth-century emergence of new perspectives on organic nature, perspectives

based on history and specifically on developmental history.

1 Baer was born in Estonia. Between 1817 and 1834 he lived in Konigsberg, teaching and researching in

zoology, anatomy and anthropology. It was during this period that he carried out his renowned

embryological studies. In 1834, he moved to the Russian Academy of Sciences in St Petersburg, where he

remained until his retirement. On Baer’s life and work see, for example, von Baer (1866), Raikov (1968),

Breidbach in Baer (1999, pp. vii–ix), Breidbach and Ghiselin in Baer (2006, pp. v–xxvii), Schmuck

(2009, pp. 115–188) and Riha and Schmuck (2011). Here and throughout, all translations are my own

unless otherwise attributed.2 Francois Jacob also contributed to this picture, although in his account the transformation begins

earlier, in the eighteenth century (Jacob 1993, pp. 130–152).

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The questions I raise here pick up on several studies that have explicitly or

implicitly queried the historiographical narrative of a ‘‘temporalization of nature’’

around 1800. Arno Seifert, for instance, has radically questioned the notion of an

atemporal premodern knowledge of nature. Seifert demonstrates that diachronic

histories of nature were in fact formulated in early modernity; he argues that

eighteenth-century naturalists and philosophers reverted to these earlier diachronic

histories but interpreted them in radically new ways. Rather than setting a

premodern, atemporal view of nature against a modern, temporal one, Seifert thus

distinguishes between various ways of envisioning the historicities and temporal-

ities of nature that arose throughout the early modern period (Seifert 1983; see also

Stockhorst 2006). Other scholars have worked on the case of Buffon to produce a

highly differentiated picture of the eighteenth-century concept of time and history

(Rheinberger 1990; Hoquet 2010). Hans-Jorg Rheinberger shows that Buffon, the

author of the Histoire naturelle (1749–1788), certainly did conceive of temporal

changes in organic nature, but did not regard the principle of change as inherent to

nature. For Buffon, Rheinberger concludes, the organic world was ‘‘subject to the

regime of time, but without history’’ (Rheinberger 1990, p. 221). Another far-

reaching critique of the ‘‘temporalization of nature’’ hypothesis is offered by Janina

Wellmann in her cultural history of embryology between 1760 and 1830. Wellmann

argues that the epistemological innovation around 1800 was not simply ‘‘time

bursting into the world of the organic;’’ in examples that include Baer’s description

of the chick embryo’s formation in the first volume of Entwicklungsgeschichte der

Thiere. Beobachtung und Reflexion (von Baer 1828/1999), she identifies the

emergence of a new structure and order of time that she describes as ‘‘rhythm’’

(Wellmann 2010, p. 373; see also Wellmann in this issue). The historians Dietrich

von Engelhardt and Peter Hanns Reill have contrasted the concept of history and

time that took shape around 1800 in the context of Naturphilosophie with the one

that prevailed during the Enlightenment (von Engelhardt 1979, 1988, 1990; Reill

2005). Reill argues that the Naturphilosophen differed from Enlightenment

naturalists in rejecting linear change and development. Instead, their visions of

organic nature were formed by ideas of circular processes and the return to origins.

Reill interprets the attempts of the Naturphilosophen ‘‘to eliminate or minimize the

temporal and epistemological uncertainties of a fully historicized world’’ as a

reaction against the French Revolution, which they experienced as a source of

uncertainty and chaos (Reill 2005, p. 220). He further shows that Naturphiloso-

phie’s call for the renewal of order and clarity transformed the epigenetic theories of

generation formulated by Enlightenment naturalists. Notions of ambiguity and

equality between the sexes gave way to those of gender polarity and hierarchy (see

Reill 2005, pp. 220–236; Lettow 2014; Vienne 2014).

In this historiographical context, it becomes important to ask after the concept of

developmental history underlying Baer’s early nineteenth-century research. With a

micro-analysis of his 1827 study of the mammalian egg, I begin by describing in

more detail Baer’s understanding of development, history, and time. Continuing

Reill’s line of thought, I also analyse the concept of gender difference upon which

Baer’s new vision of the process of organic formation rested. To what extent did

early nineteenth-century embryologists and physiologists continue the efforts of the

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Naturphilosophen to reinterpret generation in terms of a gender dichotomy? To

answer this question, I confront Baer’s study of the mammalian egg with other

explanations of embryogenesis that arose in the 1820s and 1830s, especially the

studies of fertilization carried out jointly by the French scholar Jean-Baptiste Dumas

(1800–1884) and the Swiss Jean-Louis Prevost (1790–1850) and the new

interpretation of generation by Theodor Schwann (1810–1884) based on cell

theory. As we will see, these researchers reached widely divergent conclusions on

the meaning of gender difference in generation, divergences that were associated

with different models of developmental history. My key hypothesis is that the 1820s

and 1830s saw the emergence of very different, and sometimes contradictory, forms

of thought and research in developmental history. In this sense, I contest Timothy

Lenoir’s assumption that biology issued from a unified ‘‘historical way of seeing’’

(Lenoir 1985, p. 100; see also Lenoir 1990) and a monolithic research programme

that he characterizes as ‘‘teleo-mechanist’’ (Lenoir 1982, p. 12). I would also dispute

the image presented by many historians of biology that a straight line of

development led from the developmental-history approaches of the late eighteenth

and early nineteenth century up to the formulation of cell theory (see Temkin 1950,

p. 237; Balan 1979, pp. 281–285; Duchesneau 1987, pp. 113–128; Lenoir 1982,

pp. 112–134; Jacyna 1990; Parnes 2000). This image largely accords with the

interpretation put forward by Foucault and Lepenies that, in the 1820s, ‘‘the

historical point of view’’ (Lepenies 1976, p. 16; my emphasis) came to prevail in

science once and for all, bringing with it the end of natural history.3 My own

conclusion is that the emergence of developmental-history perspectives in the first

third of the nineteenth century was far from putting an end to the whole range of the

static, classifying approaches and objects of natural history.

2 Change and continuity: Baer’s concept of developmental history

In his 1821 address on the ‘‘current state of natural history,’’ Baer contrasted his

sarcastic portrait of endlessly proliferating descriptions of nature with comparative

anatomy (especially the work of Cuvier) and Naturphilosophie. In Baer’s view,

these had both embarked upon a new way of looking at nature, the highest goal of

which was to investigate ‘‘the laws of organic formation’’ (von Baer 1821, p. 40).4

Baer intended the exploration of these ‘‘laws’’ to encompass not only processes of

becoming and passing away, but also—and especially—the eternal or unchanging

aspect of nature. This becomes very clear in another of his lectures, held in 1822:

‘‘The idea, or what is essential, what is living in animals is eternal, merely passing

through a series of different individuals in which it is always independently realized.

3 Lepenies borrows Foucault’s time frame, which locates the transition from natural history to biology in

the period between 1775 and 1825 (Foucault 1974, p. 221).4 In his memoirs, Baer claimed only to have ‘‘fully studied’’ Oken’s ‘‘natural philosophy,’’ having had

neither the time nor the interest for exhaustive consideration of the works of Schelling and other natural

philosophers (von Baer 1866, pp. 289–290, also 170–171). There are various interpretations of Baer’s

relationship with Naturphilosophie. See, among others, Riha and Schmuck (2011, pp. 230–233); Lenoir

(1982, pp. 85–86).

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Thus, the law prevails in nature that the various forms of organic bodies are always

preserved whereas the individuals always perish’’ (Baer 1822, p. 63).5 Baer’s words

may be read as a programmatic statement prefiguring his famous embryological

studies of subsequent years. He argues that the research carried out hitherto—

whether based on preexistence theory or the theory of epigenesis—has been too

strongly oriented on the search for a ‘‘specific beginning, a sharp boundary between

being and nonbeing.’’ Yet, Baer continues, ‘‘nature shows us no such boundary

anywhere. At every moment she has something new, but, upon closer inspection,

what is new always reveals itself to be merely a transformation of something that

went before; nowhere does nature’s workshop show us a series of works that she has

begun from the very beginning. Ingenuity and imagination have therefore been

stretched to the limit in the attempt to detect this moment’’ (Baer 1822, p. 60). For

Baer, then, changing the trajectory of research on generation meant seeing the

formation of a new organism no longer simply as the beginning of an individual

existence, but as part of a larger, unending organic process. In this section I discuss

how, and with what epistemological implications, Baer put this programme into

practice with his embryological research.

In 1822, Baer offered his audience a developmental history of the bird’s egg that

was based neither on the assumption that the embryo was preformed nor that it took

shape suddenly out of unformed material. He picked up on a study of the formation

of the chick embryo published in 1817 by Christian Pander (1794–1865), a friend

from university days. Pander had ascribed the emergence of the embryo to ‘‘germ

layers’’ (Keimblatter) that formed in the first hours after incubation (Pander 1817),6

but Baer was not satisfied with this description of embryogenesis. He declared that

in future he would investigate earlier stages in the emergence of life: ‘‘Before the

embryo, the germ layer was in the egg. But the egg was laid by the hen. And a germ

was already present before fertilization. Fertilization is only the impetus for further

development of something that is already present; not a new beginning. Neither is

the egg a new beginning, since it develops in the hen’s ovary from other elements

also already present there. Thus, an absolute beginning is never demonstrated.

Always there is constant transformation; in their essence, the process of growth and

the process of increase are alike’’ (Baer 1822, p. 63). This objective of identifying

and describing the original elements of the process of organic formation in the ovum

found expression in Baer’s landmark study De ovi mammalium et hominis genesi of

1827.7

Baer’s treatise describes seven stages in the development of the canine ovum.

However, he begins his report not with the first of those stages, but with the

5 The only published form of this lecture is the summary by Boris Raikov (Raikov 1968), which is the

source of the following quotations.6 For detail on the context of Pander’s work and on his concept of the germ layer, see Wellmann (2010),

pp. 315–343; Schmitt (2005); Balan (1979), pp. 237–254.7 He wrote this text in Latin as an open letter to the St Petersburg Academy of Sciences, which had just

appointed him a corresponding member. The following quotations are based on the 1956 English

translation by Charles Donald O’Malley, ‘‘On the Genesis of the Ovum of Mammals and of Man’’ (von

Baer 1827/1956), or the 1927 German translation by Benno Ottow, Uber die Bildung des Eies der

Saugetiere und des Menschen (von Baer 1827/1927).

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condition of the ovum three weeks after copulation. At this point, he explains, all

the embryo’s organs can be recognized in rudimentary form. Baer traces the

development of the embryo backward from this point, but attaches a date to only

one other of the six preceding developmental stages: the ovum twelve days after

coitus (see von Baer 1827/1956, p. 151). No precise time statements are made

regarding the initial stages of development, which are the chief object of his study.

Baer’s attempt to find the original element in the process of organic formation

essentially consists in microscopic examination of the ova in their various organic

environments—in the uterus, in the tubes, and finally in the ovaries. Baer

ascertained their size, structure and component parts. Following this approach, he

‘‘opened’’ the ‘‘Graafian vesicles’’ in the ovary and ‘‘saw’’ there a structure that he

‘‘already recognized from the tubes’’ (von Baer 1827/1956, p. 132). From this

discovery, Baer concludes that alongside the Graafian vesicles (which he defines as

the ova of mammals) there is another ovum: ‘‘an ovum raised to the second power’’

(von Baer 1827/1956, p. 148), which—to avoid confusion—he also calls the

ovulum, or little egg (in the English translation ‘‘ovule,’’ in the German Eichen, von

Baer 1827/(1927), p. 15). However, in order to derive mammalian embryogenesis

from this organic entity, it would be necessary to establish whether the ovulum was

present before the Graafian vesicle. Baer admits that this question cannot be

answered by means of microscopic observation, but decides to accord priority to the

ovulum anyway (von Baer 1827/1956, p. 137). In Baer’s view, the embryo arises out

of this organized entity, and he therefore describes the ovulum as, ‘‘by reference to

the future foetus,’’ the ‘‘veritable ovum,’’ or ‘‘the foetal ovum in the maternal

ovum’’ (von Baer 1827/1956, p. 147–148).8 He triumphantly claims in the study’s

introduction to have been ‘‘fortunate enough to discover’’ the primordial beginning

of the ‘‘ovum of mammals and of man’’ (von Baer 1827/1956, p. 122). In the

developmental series portrayed in the upper part of his illustration (see Fig. 1), the

ovulum takes first place (von Baer 1827/1956, p. 150). It also features as a recurring

element at the later stages of development. Baer’s newly described organic entity

thus functions as an original—and constant—element in the process of organic

formation.

In the lower half of the plate are numerous depictions of the ovulum of various

mammals or the ‘‘vesicle of Purkinje’’ of other animals. In 1825, the Czech

physiologist Jan Evangelista Purkyne (1787–1869) had described this ‘‘vesicle’’ in

birds’ eggs as the ‘‘rudiments of the ova’’ (von Baer 1827/1956, 143). Baer

encountered Purkyne’s study in 1826, and was obviously impressed by it. As he

explained, it was a crucial concern of his own research to seek the ‘‘vesicles of

Purkinje’’ in the whole spectrum of animals, ultimately including mammals.9 His

demonstration that in mammals the process of organic formation also proceeded

from a previously organized ‘‘little body’’ (Korperchen) (von Baer 1866, p. 320; see

also von Baer 1866, pp. 310–320; von Baer 1827/1956, pp. 137, 142–148) broke

with the prevailing view that in mammals—unlike in other animals—the embryo

was formed from a female generative substance. For example, in his influential

8 In his memoirs, he also referred to the ‘‘primordial ovum’’ (von Baer 1866, p. 328).9 On Purkynes’s influence on Baer, see Knorre (1971) and Kruta (1971–1972).

Seeking the constant 39

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reference work Die Physiologie als Erfahrungswissenschaft, physiologist Karl

Friedrich Burdach (1776–1847) wrote that what arose in the mammalian ovary was

not an ovum ‘‘but merely foetal substance that, after fertilization, provides only the

first rudiments of foetal membranes and foetus …. It is thus merely a fluid that,

without its own membrane, is contained in the cells of the ovary and stretches them

into vesicles’’ (Burdach 1828, pp. 74–75). Baer’s description of the ovulum as the

Fig. 1 Illustration from ‘‘On the Genesis of the Ovum of Mammals and of Man’’ (De ovi mammalium ethomnis genesis), in: Universitatsbibliothek Giessen, Nachlass Baer, Schriften, Bd. 22, Bl. 30r

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primordial beginning of the process of formation in mammals enabled him to

attribute embryogenesis in all animals to an analogous entity. In this respect, von

Baer (1827) treatise was far more than an attempt to reinterpret the process of

organic formation in mammals. It revealed correspondences in the formation

process among the different classes of animals, and led Baer to formulate a general

law of formation: ‘‘Every animal which springs from the coition of male and female

is developed from an ovum, and none from a simple, formative liquid’’ (von Baer

1827/1956, p. 149).

However, if Baer found similarities and a certain uniformity in the process of

organic formation among the different animals, this only applied to the origins and

early stages of that process (see von Baer 1828/1999, pp. 220–221). In the first

volume of his study Uber Entwicklungsgeschichte der Thiere. Beobachtung und

Reflexion, he postulated a general law of development according to which ‘‘the

homogeneous and shared gradually gives rise to the heterogeneous and specific’’

(von Baer 1828/1999, p. 153, see also 224). With this law, Baer was countering

recapitulation theory, the dominant explanation of embryonal development in the

1820s.10 He argued that embryos, at least in ‘‘higher’’ species, did not pass through

developmental stages during which they resembled ‘‘other,’’ lower animal forms,

but differentiated in a way specific to that particular animal (von Baer 1828/1999,

p. 224). Baer thus rejected the model of linear progression, what he called a ‘‘single-

line progression’’ (von Baer 1828/1999, p. 202). Rather than allocating species to

positions in a hierarchical scale, Baer divided the animal kingdom into four ‘‘types,’’

each based on a different scheme of formation.11 The embryogenesis of each animal

was laid down from the start by its ‘‘type’’ (von Baer 1828/1999, p. 220). The notion

of predetermined and purposeful development was fundamental to Baer’s thinking.

He explicitly stressed that embryogenesis was not determined solely by the

‘‘preceding state,’’ but also guided by the ‘‘essence’’ (Wesenheit) or ‘‘idea’’ of the

future organism (von Baer 1828/1999, p. 147, 148). As already discussed, this

‘‘idea’’ stood for what remained eternally the same—in contrast to individuals,

which existed only temporarily. Interestingly, Baer also regarded ‘‘species or

generative series’’ as passing phenomena (von Baer 1833–1834/2006, p. 61). He

believed it perfectly possible that individual species would die out or be transformed

over the course of history, though he rejected the notion that all animals had

developed by evolving out of one another (von Baer 1833–1834/2006, p. 56). For

Baer, then, in organic nature developments could not arise from living material

alone.12 Processes of becoming and passing away were only partially subject to

time—and thus also to history—because ultimately they were always determined by

a higher, ideal and stable order.

10 Baer was particularly critical of the recapitulation hypothesis as formulated by Etienne Serres

(1786–1868). See Schmuck (2009, pp. 200–213) and Meyer (1935).11 ‘‘The peripheral or radial type, the jointed or extended type, the massy or mollusc type, and the type of

the vertebrates’’ (von Baer 1828/1999, 209). On Baer’s typology and the teleological thinking associated

with it, see Lenoir (1982, p. 86), Lenoir (1985), Oppenheimer (1963) and Riha and Schmuck (2011).12 Later, in the 1860s, Baer turned against Darwin’s theory of common descent. On Baer’s view of

evolution, see Brauckmann (2012), Riha and Schmuck (2011, pp. 180–212), Holmes (1947) and

Breidbach and Ghiselin in Baer 1999.

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Baer’s aspiration to discover what is continuous or ‘‘abiding’’ in the ‘‘transience’’

of organic forms (von Baer 1833–1834/2006, p. 40) shows similarities with the

concept of history and time that was moulded by the Naturphilosophen around

1800. As discussed in the introduction, they rejected linear development, sought

continuities and origins, and attributed change to ‘‘ideas’’ that remained eternally

constant (von Engelhardt 1979, pp. 111–142). However, significant differences can

be identified between Baer’s views on organic nature and those of the Naturphi-

losophen. If thinkers like Friedrich Wilhelm Schelling (1775–1854) and Lorenz

Oken (1779–1851) had redefined the eighteenth century’s epigenetic theories of

generation in line with gender dualities (see von Engelhardt 1985; Reill 2005,

pp. 220–236; Lettow 2014; Vienne 2014), I contend in the following that Baer’s

concept of development as an unending continuum and his search for general laws

of formation was accompanied by a turn away from the two-sex model. This

argument proposes a new way of reading Baer’s study of the mammalian ovum. In

the literature, no account has hitherto been taken of the fact that Baer’s ‘‘discovery

of the human ovum’’ (Schmuck 2009, p. 189) was also a response to the attempt by

two of his contemporaries to attribute embryogenesis to two different, sex-specific

generative substances.

3 Contested origins: Baer’s response to the work of Jean-Baptiste Dumasand Jean-Louis Prevost on sperm and fertilization

Immediately before Baer published his study on the mammalian egg, Dumas and

Prevost had presented their joint research on generation to the French Academy of

Sciences (see Prevost and Dumas 1821, 1824a, b, c, 1827).13 Although their work

on the physiology of generation and on embryology has attracted little attention in

the historiography of science,14 in the first two decades of the nineteenth century it

was received with interest and regarded as groundbreaking. Even in 1837, the

German physiologist Rudolf Wagner (1805–1864) still argued that it must be

‘‘regarded as the basis of all more recent investigations’’ (Wagner 1837, p. 402).

Baer knew the two men’s work. As we will see, his study on the mammalian ovum

firmly opposed their hypotheses. But what was the nature of the new perspective on

generation that Dumas and Prevost had opened up?

Unlike Baer, Dumas and Prevost did not dedicate their research exclusively to the

ovum, but also investigated seminal fluid. The first, and most significant, step in

their extensive studies on generation had been to examine the male reproductive

organs and ‘‘spermatic animals’’ of nineteen different animal species. Whereas the

13 While little is known about Prevost, Dumas entered the history books chiefly as one of the founders of

organic chemistry, alongside Justus Liebig (1803–1873). After the 1848 revolution in France, Dumas also

began a political career. He held high offices, including those of the Minister of Trade and Agriculture

and the master of the French mint. On Dumas’s life and work, see Chaigneau (1984) and Klosterman

(1985).14 Exceptions are Gasking (1967, pp. 137–147) and Farley (1982, pp. 37–42). Ilse Jahn counts Prevost

and Dumas among the founders of animal physiology, but does not mention their research on generation

(Jahn 1998, p. 350).

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majority of naturalists in the early nineteenth century believed sperm to be

microscopic animals and parasites, Dumas and Prevost established that sperm were

‘‘produced’’ in the testes (Prevost and Dumas 1821, p. 106). Their attempt to study

sperm as specific products of the male body was fundamentally new, as was their

attribution of embryogenesis to a process that had previously almost never been

analysed microscopically: fertilization. Early nineteenth-century physiologists and

embryologists equated fertilization with the act of copulation. It was new to describe

fertilization as a distinct physiological process and to ask about its relevance to

embryogenesis. Dumas and Prevost’s numerous experiments in the artificial

fertilization of frogs’ eggs showed that only those eggs exposed to seminal fluid

underwent the processes of transformation that culminated in the formation of an

embryo. To capture the significance of the changes that occurred immediately

after—and as a consequence of—fertilization, they observed the frogs’ eggs hour by

hour from the moment of fertilization onwards. They noted the changes taking place

between fertilization and the appearance of the organs, and inscribed those changes

into a developmental series that followed a chronological and linear structure.

Fertilization was the starting point, and the point of reference, for all the later

developmental stages of the ovum and embryo (see Prevost and Dumas 1824b,

pp. 107–121). In a further series of in vitro fertilization experiments, Dumas and

Prevost began to describe the process of fertilization more precisely: the spermatic

animals penetrated the mucus surrounding the ovum and thus came into ‘‘close

contact’’ with the ovum itself (Prevost and Dumas 1824c, p. 134).

Dumas and Prevost thus declared the instigator of generation to be an organic

entity—the spermatic animal—that was defined as male. Without its action, the

ovum could not develop into an embryo. As for the fortunes of the spermatic

animals after fertilization, Dumas and Prevost held different opinions. While

Prevost assumed that the spermatic animal disappeared after fertilization, Dumas

hypothesized that it went on to make a material contribution to the embryo’s

formation. For him, the spermatic animal was ‘‘nothing other than the rudiment of

the nervous system’’ (Prevost and Dumas 1827, p. 452; see also 443–454). Dumas

even succeeded in finding evidence for his claim. Studying the embryogenesis of

mammals, he had observed a ‘‘primitive line’’ twelve hours after copulation that

could not be explained in any other way than as ‘‘the rudiment of the nervous

system’’ (Prevost and Dumas 1824c, p. 132). The explanation for ‘‘inherited

similarities’’ between fathers and their offspring that Dumas had thus supplied

(Prevost and Dumas 1827, p. 452) laid the foundations for a highly consequential

scientific enterprise in the nineteenth century: the attempt to establish a material

continuity, on the level of their organic components, between the new life and both

of the sexes. As mentioned, Dumas and Prevost’s innovative results and hypotheses

were much discussed in the first decades of the century, though for the most part in

negative terms.

Baer was among the most rigorous critics of Dumas und Prevost’s theses. He and

Burdach both raised objections in Burdach’s Die Physiologie als Erfahrungswis-

senschaft. They declared it quite impossible that ‘‘the spermatic animals’’ were

‘‘originally present’’ and were produced by a ‘‘secretion’’ (Burdach 1826, p. 90, 93).

Particularly unacceptable was the notion that these animals played a role in

Seeking the constant 43

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generation and might even form the basis for the development of another organism’s

nervous system (Burdach 1826, pp. 542–543; see also von Baer 1837/1999, p. 5). In

1827, Baer’s desire to distance himself from Dumas and Prevost’s theories induced

him not merely to defend the animal and parasitic character of sperm, but to redefine

their classification within the system of nature: he assigned them to the cercariae, at

that time considered a genus of snail parasites. Because they were not identical with

these, he described them as ‘‘a very low level of the cercaria type’’ and, to avoid

ambiguity, gave them a name of their own—‘‘spermatozoa’’ (von Baer 1827,

p. 640).15 Dumas and Prevost having elevated sperm to an entity indispensable to

generation, Baer thus demoted them to the lowest ranks of a parasitic genus. And

indeed, Dumas and Prevost’s findings contradicted Baer’s view that fertilization was

not a new beginning but the continued development of something already present.

Against this background, Baer’s study of the mammalian ovum may also be read

as a response to Dumas and Prevost’s hypotheses. If Dumas and Prevost accorded

priority—in both material and temporal terms—to fertilization and the elementary

particles of the two sexes’ generative substances in the process of organic

formation, Baer ascribed no more than a secondary function to the two sexual

generative substances and the process of fertilization. As discussed in the previous

section, Baer showed firstly that in mammals as in other animals, the process of

organic formation sprang not from a generative substance, but from a ‘‘previously

organized little body.’’ What distinguished Baer’s newly described ovulum or foetal

ovum from the ‘‘Graafian vesicle’’ was precisely that, unlike the vesicle, it did not

carry any feminine connotation; as I have pointed out, Baer emphasized that it was

present prior to the ‘‘maternal ovum.’’ As such, he attributed the process of organic

formation to an entity that was not sex-specific. But the ‘‘foetal ovum’’ also existed

before the paternal semen could drive on its development into an embryo. Baer saw

the role of the male generative substance in fertilization as being to ‘‘make the idea

of the animal complete and endow it with the possibility of development’’ (von Baer

1828/1999, p. 152, see also 147–152). In contrast, he ruled out any immediate and

material paternal share in the formation of the embryo at the moment of

fertilization. Baer rejected Dumas and Prevost’s observation that the sperm entered

the ovum during fertilization (von Baer 1827/1956, p. 145). Although he reproduced

Dumas and Prevost’s description and illustration of canine ova ‘‘of twelve days’’ in

order to complete his developmental series (von Baer 1827/1956, p. 128), he did not

mention that Dumas had interpreted the ‘‘line’’ observed at this stage as signalling a

material contribution by the sperm to the construction of the new embryo.

Accordingly, at the end of his study Baer noted as a basic principle that ‘‘the male

semen acts through the membrane of the ovum [cuticula ovi], which is pervious by

no foramen, and in the ovum it acts first on certain innate parts of the ovum’’ (von

Baer 1827/1956, p. 149).

Whereas Dumas’ reinterpretation of the ‘‘spermatic animals’’ was associated with

an attempt to apprehend a material continuity between offspring and both

progenitors, Baer wanted to assert an organic continuity that went beyond the

15 The literature on Baer makes virtually no mention of his natural-history approach to sperm and its

significance for his embryological research. An exception is Riha and Schmuck (2011, pp. 179–188).

44 F. Vienne

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emergence and decay of individual organisms. For this reason, he attributed the

process of organic formation in all animals, and also in the human being, to a single

entity—the ovulum—that was regarded as independent of the female body. More

generally, Baer viewed generation not from a two-sex perspective but in terms of its

congruence with other physiological processes, especially those of ‘‘growth’’ and

‘‘nutrition.’’ For Baer, all these processes had to be understood as part of a unified

and continuous process of formation. Thus, ‘‘growth is nutrition with the formation

of new bodily mass—in fact, it is continued generation, and generation is nothing

other than the beginning of individual growth’’ (von Baer 1837/1999, p. 4). In the

late 1830s, Schwann pursued a similar point, ascribing all physiological processes in

plants and animals—including the formation of new organisms—to a unified and

universal basic unit of life: the cell. Schwann explicitly set out his concept of the

‘‘cell’’ in analogy to an ‘‘Individual, an independent Whole’’ (Schwann 1839/1847,

p. 2).16 According to him, each cell possessed ‘‘an independent life’’ and thus ‘‘a

power of its own’’ (Schwann 1839/1847, p. 192). Applied to generation, this view

conflicted with the prevailing assumption that the action of the semen was necessary

to trigger the egg’s development into an embryo. Schwann admitted that the ‘‘ova of

higher animals’’ may in fact receive something that was ‘‘more than nutrient

matter’’ through the act of fertilization. Many species, however—those comprising

‘‘female individuals only’’ and ‘‘lower plants’’ procreating without fertilization—

showed that in general each cell was an autonomous entity able to develop into a

new organism without an external stimulus (Schwann 1839/1847, p. 192). In

Schwann’s version of cell theory, thus, a male contribution was not a necessary

precondition for organic formation. While Baer accorded fertilization and the two

sexes’ generative substances a subordinate function, Schwann’s cell theory

implicitly abandoned the model of bisexual reproduction altogether.17

4 Conclusion: rethinking early nineteenth-century perspectiveson developmental history

As mentioned in this paper’s introduction, historians of biology have often

discussed how the emergence of cell theory was influenced by thinking and research

based on developmental history (see Temkin 1950, p. 237; Balan 1979,

pp. 281–285; Duchesneau 1987, pp. 113–128; Lenoir 1982, pp. 112–134; Jacyna

1990; Parnes 2000). In his history of heredity Francois Jacob argued that Baer’s

embryological work of the 1820s and the cell theory of the 1830s played a key role

in the formation of our understanding of reproduction. With these studies, according

to Jacob, procreation was no longer regarded as the production of a completely new

beings, but as the formation out of an already existing organic fragment—a basic

16 With his principle of cell autonomy, Schwann also opposed the teleological assumptions so central to

Baer’s work. There were thus also significant differences between Baer’s and Schwann’s understanding

of organic processes, which cannot be detailed here. It was Schwann’s notion of the autonomous action of

cells that Baer particularly criticized after the formulation of cell theory (von Baer 1866, pp. 380–386).17 Matthias Jacob Schleiden (1804–1881), commonly regarded as the co-founder of the late 1830s cell-

theory, held a similar view, see Farley (1982, pp. 48–51).

Seeking the constant 45

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unit of life, a ‘‘cell.’’ In his account, Jacob takes into consideration Dumas’ and

Prevost’s investigations of sperm and claims that their findings immediately and

‘‘definitively’’ established the necessity of the sperms in generation (Jacob 1993,

p. 121). My analysis shows, however, that neither Baer nor Schwann took up

Dumas’ hypothesis. More generally, the examples discussed in this paper highlight

that it is not enough to assume a single, homogeneous way of thinking based on

developmental history, or a straight line leading the way to the formulation of cell

theory and our understanding of reproduction. In the nineteenth century’s first

decades, very different forms of thinking and researching within a developmental

history frame were still arising. In particular, there were contradictory views on the

relevance of sexual difference for generation. In this period, the search for general

laws of formation and the search for a bisexual explanation of reproduction

constituted two different, and opposing, programmes of research.

What all these models of developmental history had in common, however, was

their strong focus on the ovum. Physiological studies of generation and embryo-

logical studies in the first third of the nineteenth century made the ovum the prime

category of developmental history. Regarding the sperm, in contrast, a natural-

history approach remained intact during that period. As I have shown, even in the

late 1820s Burdach and Baer were still describing the sperm using a way of thought

drawn from natural history. They were not alone in this. The dispute around the

pioneering theses of Dumas and Prevost, a debate that continued into the 1840s,

prompted their opponents to affirm and reaffirm the animal—in some cases even

parasitical—character of sperm.18 Even Dumas and Prevost’s new interpretation of

sperm as products of the male body and as reproductive units did not persuade them

to study these entities as the outcome of a process of organic formation that

unfolded step by step, or to equate them with other elementary organic units (for

example the ‘‘globules’’ of blood, which they had researched previously19). Instead,

a large portion of their research on the sperm of various animal species consisted in

describing the sperm’s shape, size, and manner of movement, as if they were

describing animals (see Prevost and Dumas 1821). Yet even the formulation of cell

theory in the late 1830s did not bring an abrupt end to spermatic animals as an

object of natural history. Although Schwann was interested in a cell-based

reinterpretation of the ovum’s structures and elements as described by Pander,

Purkyne and Baer (Schwann 1839/1847, pp. 46, 217–218), he saw no reason to

rethink the notion of spermatic animals in the light of his theory. This was because

the sperm were completely superfluous for Schwann’s law of formation, just as they

were for Baer’s explanation of embryogenesis. Research on ova and sperm in the

18 Leading German researchers in the physiology of generation in the 1830s were Rudolf Wagner

(1805–1864) and Carl Theodor von Siebold (1804–1885). They regarded sperms as the fertilizing factor

in semen, but nevertheless still as animals. See, for example, Wagner (1837), Siebold (1837). Among the

naturalists who described sperm as parasites were Carl Gustav Carus (1789–1869) (see Carus 1839) and

Gabriel Gustav Valentin (1810–1883) (see Valentin 1839).19 Dumas and Prevost’s studies of semen were preceded by research on the blood’s ‘‘globules,’’ and were

inspired by this to the extent that in both cases they were seeking the ‘‘active principle’’ of these organic

substances (Prevost and Dumas 1821, p. 196). In the historiography of biology, Dumas and Prevost have

featured as French representatives of ‘‘globule theory,’’ often considered a precursor to cell theory (Klein

1936; Pickstone 1973).

46 F. Vienne

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first third of the nineteenth century, then, was influenced in very different ways by

developmental-history approaches.

The example of Baer shows with particular clarity that the advent of new

perspectives based on developmental history by no means presupposed the collapse

of all the previous static, classifying approaches and objects of natural history. In his

1821 lecture, Baer had derided contemporary natural history in its predilection for

renaming and proliferating the names of one and the same object. Yet he himself

made his own contribution to that tradition, by renaming the ‘‘spermatic animals’’

after having redefined their location within the system of nature. The longevity of

the ‘‘spermatic animals’’ as an object of natural history in the nineteenth century

thus also shows that the relationship between natural history and biology was not

solely one of discontinuity, but also embraced continuities. The image—propagated

most notably by Foucault and Lepenies—of a radical rupture between the static,

classificatory natural history of premodern times and the historical biology of

modernity may obscure our view of the continuities between these two forms of

knowledge about nature. The concept of sperm propounded by natural history, for

example, seems never to have faded completely; in an altered form it has

contributed to our modern understanding of the male germ cell. At the very least,

the label ‘‘spermatozoa’’ introduced by Baer has survived. At the time when he

coined this term, Baer mocked the idea that during fertilization ‘‘millions of such

spermatic animals battle murderously until the one that is left enters the vesicle of

the female ovary as a triumphant victor’’ (von Baer 1837/1999, p. 5). Yet it is that

very idea which we encounter again in today’s cellular understanding of

fertilization.

Translated by Kate Sturge

References

Balan, B. (1979). L’ordre et le temps. L’anatomie comparee et l’hsitoire des vivants au XIXe siecle. Paris:

Vrin.

Brauckmann, S. (2012). Karl Ernst von Baer (1792–1876) and evolution. International Journal of

Developmental Biology, 56, 653–660.

Burdach, K. F. (1826). Die Physiologie als Erfahrungswissenschaft (Vol. 1). Leipzig: Leopold Voss.

Burdach, K. F. (1828). Die Physiologie als Erfahrungswissenschaft (Vol. 2). Leipzig: Leopold Voss.

Carus, C. G. (1839). Needhamia expulsoria sepiae officinalis. Verhandlungen der kaiserlichen

leopoldinisch-carolinischen Akademie der Naturforscher, 11, 1–19.

Chaigneau, M. (1984). Jean-Baptiste Dumas, sa vie, son oeuvre 1800–1884. Paris: Guy Le Prat.

Duchesneau, F. (1987). Genese de la theorie cellulaire. Montreal: Bellarmin, Vrin.

Farley, J. (1982). Gametes & spores. Ideas about sexual reproduction. Baltimore: Johns Hopkins

University Press.

Foucault, M. (1974). The order of things: An archaeology of the human sciences. London: Routledge.

Gasking, E. (1967). Investigations into generation 1651–1828. London: Hutchinson.

Holmes, S. J. (1947). K. E. Von Baer’s perplexities over evolution. Isis, 37, 7–14.

Hoquet, T. (2010). History without time. Buffon’s natural history as a nonmathematical physique. Isis,

101, 30–61.

Jacob, F. (1993). The logic of life. A history of heredity (B. E. Spillmann, Trans.). Princeton: Princeton

University Press.

Seeking the constant 47

123

Jacyna, L. S. (1990). Romantic thought and the origins of cell theory. In A. Cunningham & C. Jardine

(Eds.), Romanticism and the sciences (pp. 160–168). Cambridge: Cambridge University Press.

Jahn, I. (Ed.). (1998). Geschichte der Biologie: Theorien, Methoden, Institutionen, Kurzbiographien (3rd

ed.). Jena: Fischer.

Klein, M. (1936). Histoire des origines de la theorie cellulaire. Paris: Hermann & cie.

Klosterman, L. J. (1985). A research school of chemistry in the nineteenth century: Jean Baptiste Dumas

and his research students. Parts I and II. Annals of Science, 42, 1–80.

Knorre, H. (1971). Die Entstehungsgeschichte von K. E. Baers ‘Sendschreiben’: De ovi mammalium et

hominis genesi 1827 und vier Briefe Karl Ernst von Baer an Carl Asmund Rudolphi. Leopoldina, 17,

237–286.

Kruta, V., (1971–1972). K. E. von Baer and J. E. Purkyne. An analysis of their relations as reflected in

their unpublished letters. Lychnos. Annual of The Swedish History of Science Society, 93–120.

Lenoir, T. (1982). The strategy of life. Teleology and mechanics in nineteeth-century German biology.

Chicago: Chicago University Press.

Lenoir, T. (1985). Kant, von Baer und das kausal-historische Denken in der Biologie. Berichte zur

Wissenschaftsgeschichte, 8, 99–114.

Lenoir, T. (1990). Morphotypes and the historical-genetic method in Romantic biology. In A.

Cunningham & C. Jardine (Eds.), Romanticism and the sciences (pp. 119–129). Cambridge:

Cambridge University Press.

Lepenies, W. (1976). Das Ende der Naturgeschichte. Wandel kultureller Selbstverstandlichkeiten in den

Wissenschaften des 18. und 19. Jahrhunderts. Munich: Hanser.

Lettow, S. (2014). Generation, genealogy and time: The concept of reproduction from histoire naturelle to

naturphilosophie. In S. Lettow (Ed.), Gender, race and reproduction. Philosophy and the early life

sciences in context (pp. 21–43). Albany: SUNY Press.

Meyer, A. W. (1935). Some historical aspects of the recapitulation idea. The Quarterly Review of Biology,

10, 379–396.

Oppenheimer, J. M. (1963). K. E. von Baer’s beginning insights into causal-analytical relationships

during development. Developmental Biology, 7, 11–21.

Pander, C. (1817). Beitrage zur Entwicklungsgeschichte des Huhnchens im Eye. Wurzburg: Bronner.

Parnes, O. (2000). Envisioning the cell. Science in Context, 13, 71–92.

Pickstone, J. V. (1973). Globules and coagula. Concepts of tissue formation in the early nineteenth

century. Journal of the History of Medicine, 28, 336–356.

Prevost, J.-L., & Dumas, J.-B. (1821). Essai. Sur les Animalcules spermatiques de divers Animaux.

Memoires de la Societe de Physique et d’Histoire Naturelle de Geneve, 1, 180–207.

Prevost, J.-L., & Dumas, J.-B. (1824a). Nouvelle theorie de la generation. Annales des Sciences

Naturelles, 1, 1–28.

Prevost, J.-L., & Dumas, J.-B. (1824b). Deuxieme Memoire sur la Generation. Rapports de l’oeuf avec la

liqueur fecondante. Phenomenes appreciables, resultant de leur action mutuelle. Developpement de

l’oeuf des Batraciens. Annales des Sciences Naturelles, 2, 100–121, 129–149.

Prevost, J.-L., & Dumas, J.-B. (1824c). Troisieme Memoire. De la generation dans les Mammiferes, et les

premiers indices de developpement de l’Embryon. Annales des Sciences Naturelles, 3, 113–138.

Prevost, J.-L., & Dumas, J.-B. (1827). Memoire sur le developpement du Poulet dans l’oeuf. Annales des

Sciences Naturelles, 12, 415–454.

Raikov, B. E. (1968). Karl Ernst von Baer 1792–1876. Sein Leben und sein Werk (H. von Knorre, Trans.).

Leipzig: Johann A. Barth.

Reill, P. H. (2005). Vitalizing nature in the enlightenment. Berkeley: University of California Press.

Rheinberger, H.-J. (1990). Buffon: Zeit, Veranderung und Geschichte. History and Philosophy of the Life

Sciences, 12, 203–223.

Riha, O., & Schmuck, T. (2011). ‘‘Das allgemeinste Gesetz.’’ Karl Ernst von Baer (1792–1876) und die

großen Diskurse des 19. Jahrhunderts. Aachen: Shaker Verlag.

Schmitt, S. (2005). From eggs to fossils: Epigenesis and transformation of species in Pander’s biology.

International Journal of Developmental Biology, 49, 1–8.

Schmuck, T. (2009). Baltische Genesis. Die Grundlagen der Embryologie im 19. Jahrhundert. Aachen:

Shaker Verlag.

Schwann, T. [1839] (1847). Microscopical researches into the accordance in the structure and growth of

animals and plants (H. Smith, Trans.). London: Printed for the Sydenham Society.

Seifert, A. (1983). ‘Verzeitlichung’. Zur Kritik einer neueren Fruhneuzeitkategorie. Zeitschrift fur

historische Forschung, 10, 447–477.

48 F. Vienne

123

Siebold, C. T. (1837). Fernere Beobachtungen uber die Spermatozoen der wirbellosen Thiere. Archiv fur

Anatomie, Physiologie und wissenschaftliche Medicin, 1837, 382–391.

Stockhorst, S. (2006). Zeitkonzepte. Zur Pluralisierung des Zeitdiskurses im langen 18. Jahrhundert. Das

achtzehnte Jahrhundert. Zeitschrift der Deutschen Gesellschaft zur Erforschung des achtzehnten

Jahrhunderts, 30, 157–164.

Temkin, O. (1950). German concepts of ontogeny and history around 1800. Bulletin of the History of

Medicine, 24, 227–246.

Valentin, G. (1839). Uber die Spermatozoen des Baren. Verhandlungen der kaiserlichen leopoldinisch-

carolinischen Akademie der Naturforscher, 11, 237–244.

Vienne, F. (2014). Organic molecules, parasites, ‘Urthiere’: The contested nature of spermatic

animalcules, 1749–1841. In S. Lettow (Ed.), Gender, race and reproduction. Philosophy and the

early life sciences in context (pp. 45–63). Albany: SUNY Press.

von Baer, K. E. (1821). Zwei Worte uber den jetzigen Zustand der Naturgeschichte. Vortrage bei

Gelegenheit der Errichtung eines zoologischen Museum zu Konigsberg. Konigsberg: Gebruder

Borntrager.

von Baer, K. E. (1822). Vorlesung uber die Zeugung. In B. E. Raikov (Ed.), Karl Ernst von Baer 1792–

1876. Sein Leben und sein Werk (pp. 60–64, H. von Knorre, Trans.). Leipzig: Johann A. Barth.

von Baer, K. E. (1827). Beitrage zur Kenntnis der niederen Tiere. Verhandlungen der Kaiserlichen

Leopoldinischen Carolinischen Akademie der Naturforscher, 13, 523–762.

von Baer, K. E. (1866). Nachrichten uber Leben und Schriften des Herrn Geheimraths Dr. Karl Ernst von

Baer, mitgeteilt von ihm selbst; veroffentlicht bei Gelegenheit seines funfzigjahrigen Doctor-

Jubilaums am 29. August 1864 von der Ritterschaft Ehstlands, St Petersburg: Verlag der koniglichen

Hofbuchhandlung.

von Baer, K. E. [1827] (1927). Uber die Bildung des Eies der Saugetiere und des Menschen. Ein

Sendeschreiben and die Kaiserliche Akademie der Wissenschaften zu Petersburg (B. Ottow, Ed.,

Trans.). Leipzig: Leopold Voss.

von Baer, K. E. [1827] (1956). On the genesis of the ovum of mammals and of man, trans. C.D.

O’Malley. Isis, 47(2), 117–153.

von Baer, K. E. [1828/1837] (1999). Uber Entwickelungsgeschichte der Thiere: Beobachtung und

Reflexion (O. Breidbach, Ed.). Facsimile reprint of the Konigsberg 1828–1837 edition. Hildesheim:

Olms-Weidmann.

von Baer K. E. [1833–1834] (2006). Das allgemeine Gesetz der Natur in aller Entwicklung. Ein Vortrag

gehalten in der physikalisch-okonomischen Gesellschaft zu Konigsberg. In K. E. Baer, O.

Breidbach, & M. Ghiselin (Ed.), Reden und kleinere Aufsatze (pp. 37–74). Hildesheim: Olms-

Weidmann.

von Engelhardt, D. (1979). Historisches Bewußtsein in der Naturwissenschaft: von der Aufklarung bis

zum Positivismus. Freiburg: Alber.

von Engelhardt, D. (1985). Die organische Natur und die Lebenswissenschaften in Schellings

Naturphilosophie. In R. Heckmann, K. Hermann, & R. W. Meyer (Eds.), Natur und Subjektivitat.

Zur Auseinandersetzung mit der Naturphilosophie des jungen Schelling; Referate, Voten u.

Protokolle der II. Internationalen Schelling-Tagung Zurick 1983 (pp. 39–57). Stuttgart: Frommann-

Holzboog.

von Engelhardt, D. (1988). Die Naturwissenschaft der Aufklarung und die romantisch-idealistische

Naturphilosophie. In C. J. Jamme, & G. Kurz (Eds.), Idealismus und Aufklarung. Kontinuitat und

Kritik der Aufklarung in Philosophie und Poesie um 1800 (pp. 80–96). Stuttgart: Klett-Cotta.

von Engelhardt, D. (1990). Historical consciousness in the German Romantic Naturforschung. In A.

Cunningham & C. Jardine (Eds.), Romanticism and the sciences (pp. 55–68). Cambridge:

Cambridge University Press.

Wagner, R. (1837). Fragmente zur Physiologie der Zeugung vorzuglich zur mikroskopischen Analyse des

Sperma’s. Abhandlungen der mathematisch-physikalischen Classe der Koniglichen Akademie der

Wissenschaften, 2, 381–415.

Wellmann, J. (2010). Die Form des Werdens. Eine Kulturgeschichte der Embryologie, 1760–1830.

Gottingen: Wallstein.

Seeking the constant 49

123