io8 Phenomena Refuting Simple Epigenesis 



formistic germs, would nevertheless be formed of a 

 greater or less number of specific parts different from 

 one another. 



Of all these hypotheses which one can form concern- 

 ing the nature of the developmental process and the 

 structure of the germinal substance, we need discuss here 

 only the following chief ones, and consider these only 

 very briefly, mentioning the others only casually in 

 passing. We arrange them in the following way: 



Concerning the nature of the developmental process : 



1. Simple epigenesis with preformistic germs or 

 without such. 



2. Evolution with preformistic germs, i. e., pre- 

 formation proper. 



Concerning the structure of the germinal substance : 



1. Germinal substance consisting of homogeneous 

 material. 



2. Germinal substance consisting of heterogeneous 

 material. Here belongs the special case in which this 

 substance consists of preformistic germs. 



We can now pass on without further comment to a 

 rapid review of the most important phenomena, on 

 account of which simple epigenesis with preformistic 

 germs or without such, cannot be admitted. This will 

 oblige us sometimes to return to the phenomena and 

 arguments with which we were occupied in the preceding 

 chapter. 



With the chief facts which are opposed to simple 

 epigenesis we must now range the production, already 

 mentioned and discussed, of right and left, anterior and 

 posterior, half embryos of frogs, which resulted from 

 the killing by a hot needle of one of the two first 



