54 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



At the end of organogenesis the structure is assumed to 

 have been broken up into its elements, and these elements, 

 which may be chemical compounds, determine the fate of 

 the single cells of the adult organism. 



Here let us pause for a moment. There cannot be any 

 doubt that Weismann's theory resembles to a very high 

 degree the old " evolutio " doctrines of the eighteenth 

 century, except that it is a little less crude. The chick itself 

 is not supposed to be present in the hen's egg before develop- 

 ment, and ontogeny is not regarded as a mere growth of 

 that chick in miniature, but what really is supposed to be 

 present in the egg is nevertheless a something that in all its 

 parts corresponds to all the parts of the chick, only under 

 a somewhat different aspect, while all the relations of the 

 parts of the one correspond to the relations of the parts 

 of the other. Indeed, only on such an hypothesis of a 

 fairly fixed and rigid relation between the parts of the 

 morphogenetic structure could it be possible for the 

 disintegration of the structure to go on, not by parts of 

 organisation, but by parts of symmetry ; which, indeed, is 

 a very strange, but not an illogical, feature of Weismann's 

 doctrine. 



Weismann is absolutely convinced that there must be 

 a theory of " evolutio," in the old sense of the word, to 

 account for the ontogenetic facts ; that " epigenesis " has its 

 place only in descriptive embryology, where, indeed, as we 

 know, manifoldness in the visible sense is produced, but 

 that epigenesis can never form the foundation of a real 

 morphogenetic theory : theoretically one pre-existing mani- 

 foldness is transformed into the other. An epigenetic 

 theory would lead right beyond natural science, Weismann 



