io6 Phenomena Refuting Simple Epigenesis 



hypothesis, this influence is, on the contrary, of the very 

 greatest importance and is considered to be the only 

 cause of each development. 



We also can accept Mivart's definition in this sense. 

 We note that it does not include in any way the con- 

 ception of preformistic germs; for it is possible that the 

 internal causes involved arise gradually in the course of 

 development and need not be already present in the germ 

 substance. In the first case, one has evolution without 

 preformistic germs; in the latter, evolution with pre- 

 formistic germs, which we would call pre formation 

 proper. This pre formation proper, for example Weis- 

 mann's type, is also included in the definition of evolution 

 just given; it forms however only a special case of it, 

 which is limited and approximates more the conception of 

 pre formation which the ovists and spermatists enter- 

 tained. 



The processes of epigenetic nature can be regarded 

 likewise as belonging to two kinds, corresponding to the 

 above mentioned categories of evolution. For one can 

 conceive of processes of epigenetic nature both with pre- 

 formistic germs and without preformistic germs, and 

 both cases are actually met with. 



In the first case the causes which bring about each 

 specificity of development would be already present in 

 the germinal substance. Only their liberation or acti- 

 vation in opportune time and place depends upon the 

 reciprocal action of the different parts of the organism 

 upon one another (for example DeVries, Oscar Hertwig, 

 etc.). In the second, on the contrary, the causes pro- 

 ducing the different specificities of development arise only 

 gradually in the course of ontogeny, and always in con- 



