Section I 

 PROBLEMS, CONCEPTS AND THEIR HISTORY 



JANE M. OPPENHEIMER* 



"Is cell-differentiation inherent or induced? 



"A thoughtful and distinguished naturalist tells 

 us that while the diffei-entiation of the cells which 

 arise from the egg is sometimes inherent in the egg, 

 and sometimes induced by the conditions of develop- 

 ment, it is more commonly mixed; but may it not 

 be the mind of the embryologist, and not the natu- 

 ral world, that is mixed? Science does not deal in 

 compromises, but in discoveries. When we say the 

 development of the egg is inherent, must we not 

 also say what are the relations with reference to 

 which it is inherent? When we say it is induced, 

 must we not also say what are the relations with 

 reference to which it is induced? Is there any way 

 to find this out except scientific discovery?" 



W. K. Brooks ('02, pp. 490-491) 



It is the self-imposed task of the present 

 compendium to review and evaluate the past 

 and present accomplishments of the science 

 of embryology in order more intelligently to 

 facilitate progress into its future. The sepa- 

 rate contributions which make up the main 

 body of the volume must necessarily concen- 

 trate on particular fields of investigation. It 

 is the purpose, therefore, of the first two 

 chapters to provide a general background 

 against which these more special subjects 

 may be considered. Out of convenience, 

 rather than from logical necessity, these two 

 chapters will concern themselves first with 

 concepts, and secondly with techniques, 

 though the nature of the scientific method 

 is such that these two aspects of the prob- 

 lem are inextricably interrelated. Arbitrar- 

 ily, too, the topics chosen for discussion will 

 be selective rather than exhaustive; since it 

 is not possible in a few pages to do justice to 

 even a few of the great contributors of the 

 past, only those have been chosen whose 

 writings are most relevant to the sequel, and 



* The writing of Sections I and II was carried out 

 both at the Osborn Zoological Laboratory, Yale 

 University, and at Bryn Mawr College. I owe espe- 

 cial gratitude to the Library of the College of Phy- 

 sicians of Philadelphia for the use of their collec- 

 tions and for generous assistance. 



even of these, many can enjoy only the bar- 

 est mention. 



THE EARLY EMBRYOLOGY OF THE 

 GREEKS: ARISTOTLE 



Since it was the Greeks who performed the 

 great tour de force of freeing science from 

 magic and elevating it into the realms of 

 pure reason, it is sensible to begin by exam- 

 ining a few of their contributions to embry- 

 ology. They were early to develop an inter- 

 est in beginnings; their very word for nature 

 {(puats, physis) according to some, including 

 Aristotle (Parts of Animals, 1945 edition, pp. 

 74^75), implies growth, genesis or origin 

 ((pveadai), and Anaximander, who flour- 

 ished in the sixth century B.C., spoke of the 

 yovinov., the germ or fetus of the world. 

 They recognized early that change was an 

 essence of existence, as we know from Hera- 

 kleitos' emphasis on flux, and as is evident 

 from their mythological conception of cos- 

 mos evolving from chaos. And from the be- 

 ginning they compared cosmos to the organ- 

 ism, witness Plato {Timaeus, [1944] edi- 

 tion, p. 117): 



Its composing artificer constituted it from all 

 fire, water, air, and earth; leaving no part of any 

 one of these, nor any power external to the world. 

 For by a reasoning process he concluded that it 

 would thus be a whole animal, in the highest de- 

 gree perfect from perfect parts. 



But more than this, perhaps even because 

 of it, they were able even as early as the 

 time of Anaximander to conceive of the or- 

 ganism as emergent, and indeed of animals 

 as related to man: a fragment concerning 

 the teachings of Anaximander reads that 

 "living creatures arose from the moist ele- 

 ment, as it was evaporated by the siui. Man 

 was like another animal, namely, a fish, in 

 the beginning" (Burnet, '30, p. 70). 



No attempt can be made here to enumer- 

 ate the many Greek philosophers to build 

 upon these beginnings, or to evaluate the 



