106 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 preformation 
proper. This preformation 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 
preformation 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- 
