108 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 
