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THE AMERICAN NATURALIST [Vol. XLIX 



ing on these problems, has been recognized for some time. 2 

 The considerations to be presented in the papers of this 

 series are in part the outgrowth of experimental work 

 on the central nervous system and its relation to the proc- 

 esses of evolution ; 3 they were in part suggested by Black- 

 man 's 4 paper on the manifestations of the principles of 

 chemical mechanics in living matter ; and they have grad- 

 ually grown up in our minds as our attention was at- 

 tracted more and more to the questions involved. The 

 bearing upon the processes of evolution of certain of the 

 facts drawn from the experimental study of the compara- 

 tive physiology of the nervous system will, for the most 

 part, be presented in separate papers embodying the 

 experimental data. The relation of the physico-chemical 

 conditions of the organism, together with those nervous 

 mechanisms with which the maintenance of the physico- 

 chemical conditions is inextricably bound up, to the ques- 

 tions of adaptation and fitness of the organism will con- 

 stitute the greater part of the subject matter of this and 

 following papers on the general problems of evolution 

 from the point of view of the physiologist. 



Since the inception of the work, there have appeared, 

 in addition to Blackman's paper, several other papers of 

 interest to physiologists on certain phases of the problem 

 of evolution. 



Woods 5 has collected the better-known cases of modi- 

 fication in animals and plants induced by changes in the 

 environment or in the general conditions of existence, as 

 shown by changes in the rate of growth, changes of the 

 external form of the body, the occurrence of artificial 



2 Howell, "Problems of Physiology of the Present Time," Congress 

 of Arts and Sciences, Universal Exposition, St. Louis, 1904, Vol. V, p. 



3 Pike. American Journal of Physiology, 1909, XXIV, p. 124; Ibid., 

 1912, XXX, p. 436; Quarterly Journal of Experimental Physiology, 1913, 



