THE FACTORS OF ORGANIC EVOLUTION. 



105 



reasoning from the tissue cell to the egg cell in order 

 to see that there is no escape from the conclusion that 

 the whole course of developmental phenomena must be 

 referred to organization of some sort. Development, 

 no less than other vital phenomena, is a function of 

 organization." 



3. A study of the phenomena of development, as 

 well as the principle of causality, make it certain that 

 all the characters of the species are pre- 

 Inherited charac- determined within the protoplasm of the 

 ters predeter- fertilized egg cell. From a frog's egg 

 mined in struc- . , ... 



ture of germ cell. onlv a fr S wl11 develop, from an echmo- 

 derm egg only an echinoderm, and the 

 course of the development is, under normal circum- 

 stances, definitely marked out in each case, even down to 

 the minutest details. All the results of experiment, as 

 well as observation and induction, only serve to render 

 this conclusion the more certain. It should be observed 

 that to affirm that characters are predetermined is a 

 very different thing from saying they are preformed. 

 The one merely asserts that the cause of the transforma- 

 tions which lead from one step to another in the devel- 

 opment is determined by the initial conditions of the 

 fertilized egg cell ; the other affirms that those trans- 

 formations have already taken place. 



The absolute determinism of development depends 

 primarily upon the constant structure of the egg cell, 

 but also to a certain extent upon a definite relation to 

 extrinsic factors. Since, however, these extrinsic fac- 

 tors may be exactly the same in two cases, and yet the 

 result of development be very different (e. g., the egg 

 of the starfish and that of the sea urchin), we can only 

 conclude that while ontogenetic differences may be 

 caused by a disturbance of the extrinsic factors, inherited 

 characters are always the result of a definite structure of 



