No. 403] 



environment, and also to the same internal influences 

 producing selection, may still, before many generations 

 have passed, adopt different methods of dealing with the 

 external environment, or introduce divergent tonus of 

 sexual or social selection, or of some other form of reflex- 

 ive selection. The divergence, in such eases, is explained 

 by the power of the species to vary, and by the proba- 

 bility that the variation will introduce new methods of 

 meeting surrounding conditions. V. W. Headley. in Ins 

 volume on "Problems of Evolution" (on pp. 146- 149), 

 gives illustrations of how branches of the same species 

 may adopt "alternative methods of adjustment to thr 

 same environment/' and yet in the same book (on p. 

 103) we read: "If the environment remains unchanged, 

 evolution ceases," and on p. 153— "Nothing but change 

 of environment can lead to further evolution. " His mind 

 seems to cling to the old statements of general laws, 

 though he has come to recognize a class of facts that are 

 quite at variance with these old statements. 



It therefore appears that we need not only a clear and 



