CHAPTER XII 



ADAPTATION TO ENVIRONMENT 



I. It is assumed by certain biologists that the envir- 

 onment influences the organism in such a way as to 

 increase its adaptation. Were this correct it would 

 not contradict a purely physicochemical conception of 

 life ; it would only call for an explanation of the me- 

 chanism by which the adaptation is brought about. 

 There are striking cases on record which warn us 

 against the universal correctness of the view that 

 the environment causes an adaptive modification of 

 the organism. Thus the writer pointed out in 1889 

 that positive heliotropism occurs in organisms which 

 have no opportunity to make use of it,' e. g., Cuma 

 rathkii, a crustacean living in the mud, and the 

 caterpillars of the willow borer living under the bark 

 of the trees. We understand today why this should 

 be so, since heliotropism depends upon the presence of 

 photosensitive substances, and it can readily be seen 



» Loeb, J., Der Heliotropismus der Tiere und seine Ubereinstimmung 

 tnit dem Heliotropismus der Pflanzen. Wurzburg, 1890 (appeared in 

 1889). 



318 



