242 SECTION F. 



accept neither of the sugg-estions which have been offered. Useful indi- 

 vidual modiflcations are not directly due to the external forces and are 

 not due to the inherent constitution of the organism. 



The only remaining hypothesis is that which I have already mentioned 

 — thevievpthat whenever organisms react adaptively under external forces 

 they do so because of special powers conferred on them by natural selec- 

 tion. This hypothesis will, it seems to me, meet and satisfactorily ex- 

 plain all the facts of the case — whether employed as a preparation or as 

 a substitute for hereditary variations accumulated by Natural Selection. 



In closing the discussion, in reply to Professor Poulton, Professor 

 Osborn stated that natural selectionists vpere wont to embrace every new 

 process discovered in nature in the old comprehensive power of selection ; 

 but that he believed that plastic adaptation had not been acquired by 

 Natural Selection but was a fundamental propei'ty of protoplasm. 



