22 



GENERAL EMBRYOLOGY 



expand, or to unfold and grow, to produce the individual of 

 the next generation. The relation between the germ and the 

 adult seemed much like that between the bud and the branch 

 all the parts present in minute rudiments, ready to come forth 

 and expand. We may recognize in this idea a morphological 

 conception of development such as we should expect to appear 

 first. This conception, with which are associated such great 

 names as Malpighi, Bonnet, and Haller, 

 proves in reality an attempt to explain 

 development by denying its occurrence. For 

 the assumed formation of the original indi- 

 viduals of a species by the Creator involved 

 at the same time the creation, within them, 

 of the preformed germs of all the other later 

 individuals of the species. The belief that 

 the germ cells of an organism contained in 

 miniature the members of the second genera- 

 tion necessitated the further belief that in 

 these latter must be contained, within still 

 smaller limits, the individuals of the third 

 generation, and thus ad infinitum. And so it 

 was estimated that some two hundred mil- 

 lions of human beings were actually contained 



FIG. 12. Draw- 3 . J 



ing of a human in this preformed condition within the ovaries 



sperm cell contain- Q Eye rp^ concept i on Q f infinite CUCaSC- 

 ing a miniature or- 



ganism enclosed in ment or " embditement" proved to be the 



a thin membrane. 7 . . 77 7 fj-iji 



After o. Hertwig, Teductio ad absurdum of the theory of pre- 

 Hartsoeker formation nn this its first and crudest form. 



Those who actually observed the chick ap- 

 pear within the egg could not accept this naive explanation of 

 development, but believed that there occurred a true formation 

 of parts anew out of unformed material not possessing at all 

 the characters of the adult organism. This was Wolff's idea of 

 epigenesis, clearly a physiological conception of development, 

 following quite naturally the earlier morphological conception. 

 In its original form epigenesis was chiefly a dissent from the 

 idea of preformation rather than an explanation of develop- 



