DEVELOPMENT OF BIOLOGY 



467 



sion of Malpighi, however, was seized upon by contemporary 

 biologists. Apparently, unbeknown to him, some of the eggs which 

 he studied were slightly incubated, so that he thought traces of the 

 future organism were preformed in the egg. This error contributed 

 to the formulation of the preformation theory, which gradually 

 became the dominant question in embryology. (Page 274.) 



As a matter of fact the time was not ripe for theories of develop- 

 ment. The preformationists were wrong, but so were Aristotle, 

 Harvey, and later supporters of epigenesis who went to the opposite 

 extreme and denied all egg organization and therefore tried to get 



Fig. 304. — Karl Ernst von Baer. 



something out of nothing. It remained, as we know, for the present 

 generation of embryologists to work out many of the details of the 

 origin and organization of the germ cells, and to reach a level of 

 analysis deep enough to suggest how " the whole future organism is 

 potentially and materially implicit in the fertilized egg cell" and 

 thus that "the preformationist doctrine had a well-concealed 

 kernel of truth within its thick husk of error." 



The next great advance came in the accurate and comprehensive 

 studies of the Russian, von Baer (1792-1876), published in the 

 thirties of the last century. Taking his material from all the chief 

 groups of higher animals, von Baer founded comparative embry- 

 ology. Among his achievements may be mentioned: the clear 



