202 



THE AMERICAN NATURALIST 



[Vol. LIII 



Let us consider (a) the case of modification through 

 direct environmental stimuli. There is much vague talk 

 about the "environmental mould," in which the "plas- 

 tic" organism is supposed to be "cast"; but those who 

 have given much study to the subject recognize that modi- 

 fications produced by the environment are in the nature 

 of reactions to stimuli. In many cases, these reactions 

 are plainly adaptive, in the sense of furthering the life 

 or comfort of the individual or the race, as when a cal- 

 losity is developed in consequence of continued friction, 

 or an antitoxin is generated to combat a bacterial poison. 

 The fact, however, that there are varying degrees in the 

 adaptiveness of these responses, and indeed that many 

 of them appear to be wholly unadaptive, suggests the 

 prol)ability that the truly adaptive ones, when at all con- 

 stant, have resulted from the selection of "accidental" 

 variations. This can, of course, be true only of re- 

 sponses to environmental stimuli which have presented 

 themselves frequently in the history of the race. Cases 

 in which the organism has responded adaptively to stim- 

 uli quite new to racial experience are not, however, en- 

 tirely unknown. These w^ill be discussed in a later sec- 

 tion. It may l)e said in passing, however, that the only 

 conceivable scientific explanation of such cases involves 

 the principle of "trial and error," which, of course, is 

 based upon complete contingency as regards the relation 

 of means and end. 



Let us pass to (h) the effects of functioning upon the 

 functioning parts themselves. It is held by the Lamarck- 

 iaiis that organs or parts grow or diminish through use 

 and disuse, and that the perfected mechanisms whicli 



insuflicicnt analysis. (Iranting the i.arl played by vol- 

 untary action (c. exercise or practice) in the post- 



