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THE AMERICAN NATURALIST [Vol. LVI 



definite and not promiscuous, and is correlated in a remarkable 

 degree with changes in the environment. 



Have we not here a condition strikingly like what we 

 should expect to find if some factor or factors, external 

 or internal, were operating in such a way as to lessen the 

 output of some endocrinal secretion concerned in growth 

 or the determination of size? This is at least a possi- 

 bility worthy of consideration. 



In closing may I say that in what I have put before 

 you I do not pretend to have supplied the established 

 facts necessary for founding a scientific theory. The dis- 

 cussion is largely a series of suggestions, a mere work- 

 ing scheme which takes into account various phenomena 

 that appear to be related, and which in their present 

 states of disclosure seem to lend themselves to some such 

 interpretation as I have tried to give. It is presented 

 because, in my estimation, it suggests a line of thought 

 we may well entertain when we are wrestling with our 

 several problems of genetics, variation and evolution. 

 For if it can be clearly established that any one of the 

 serological influences can reach specifically from soma 

 to germ then it becomes a plausible hypothesis that many 

 of them do. If a changed or changing external or in- 

 ternal environment causes a long continued physiological 

 stress of certain parts, then as long as this stress is ac- 

 companied by changed conditions of the circulating fluids 

 of the body, so long also will the germ-cells be exposed 

 to these influences. If they are such as to induce varia- 

 tions in definite directions, orthogenesis must be the out- 

 come. 



And if serological influences play an important part in 

 adaptive somatic changes, such as adaptive hyper- 

 trophies—or for that matter, adaptive atrophies— then 

 we have the way open to conceive of how adaptive ger- 

 minal changes may likewise be the outcome of these same 

 influences. 



It is a noteworthy fact that in the geological past 

 whenever conditions suitable for new types of existence 

 occurred, new forms of life well adapted to the condi- 

 tions appeared. This has happened not only once, but 



