No. 579] PROGRESSIVE EVOLUTION 



101 



viously the one is useless without the other. An egg 

 can not develop unless it is provided with the proper en- 

 vironment at every stage. Therefore, when we say that 

 an organism inherits a particular character from its 

 parents, all we mean is that it inherits the power to pro- 

 duce that character under the influence of certain en- 

 vironmental stimuli. 5 The inheritance of the environ- 

 ment is of at least as much importance as the inheritance 

 of the material of which the organism is composed. The 

 latter, indeed, is only inherited to a very small extent, 

 for the amount of material in the egg-cell may be almost 

 infinitesimal in comparison with the amount present in 

 the adult, nearly the whole of which is captured from 

 the environment and assimilated during ontogeny. 



From this point of view the distinction between soma- 

 togenic and blastogenic characters really disappears, for 

 all the characters of the adult organism are acquired 

 afresh in each generation as a result of response to en- 

 vironmental stimuli during development. This is clearly 

 indicated by the fact that you cannot change the stimuli 

 without changing the result. 



Time forbids us to discuss the phylogenetic stages 

 through which the coelenterate passed into the ccelomate 

 type, the ccelomate into the chordate, and the chordate 

 into the primitive vertebrate. We must admit that as 

 yet we know nothing of the particular causes that de- 

 termined the actual course of evolution at each succes- 

 sive stage. What we do know, however, about the in- 

 fluence of the environment, both upon the developing 

 embryo and upon the adult, is sufficient to justify us in 

 believing that every successive modification must have 

 been due to a response on the part of the organism to 

 some environmental change. Even if the external con- 

 ditions remained practically identical throughout long 

 periods of time, we must remember that the internal 

 conditions would be different in each generation, because 



5 Compare Dr. Archdall Keid's suggestive essay on " Biological Terms " 

 (Bedrock, January, 1914). 



