THE DYNAMICS OF DISTRIBUTION 477 



variety of character than a small stretch, the conclusion we reach is that the 

 heterogeneity of organisms varies directly as the heterogeneity of the environ- 

 ment, a result which is entirely congruous with Darwinism. And that the 

 statistics are governed by probability is indicated by certain figures given on 

 p. 114, which tend to show that the mean range of the species of a genus is 

 very constant, irrespective of the size of the genus. 



Although many of Dr. Willis's data appear to be susceptible of other 

 explanations besides his own, this attempt to explore the dynamics of 

 distribution is exceedingly interesting, and is certain to give rise to much 

 controversy. 



