DARWINISM'S PRESENT STANDING. 395 



to-day motion, sensation, growth, and reproduction. This assump- 

 tion cannot meet with any serious objection unless we change our 

 ideas and definition of organic units. Granted the existence of one 

 single organic unit endowed as above, there is no reason for intro- 

 ducing further complications by the explanation of phenomena 

 through undemonstrable hypotheses, because the fact of variation in 

 organic units can be explained solely through their existence in a 

 natural world surrounded by varying conditions of existence" 

 (p. 299). 



"In the third chapter, where colour characters are used as sub- 

 jects, it is demonstrated that variation is directly produced by 

 stimuli that from relatively invariable parents, stimuli produce 

 variable offspring; and again in the fifth chapter it is shown that 

 variations arise in direct response to stimuli" (p. 300). 



"I maintain, therefore, that all organic variations are responsive 

 to stimuli, and are not due to inherent tendencies or latencies, or 

 the product of mystic elements" (p. 300). 



13 Montgomery, T. A., in a recent book of much interest ("Anal- 

 ysis of Racial Descent in Animals." 1906), explains clearly his belief 

 in the inevitable production of variation (even that called blastogenic 

 or congenital), and the influence on heredity (through this varia- 

 tion) by the influences of environment. 



14 Brooks, W. K., "The Foundations of Zoology." p. 43. i8Q9- A 

 most thoughtful and keen discussion of many of the conspicuous 

 problems of "philosophical biology," written in lucid and epigram- 

 matic style. In many ways Brooks stands at the head of American 

 philosophical biologists. 



