Characters as Adaptive and Specific. 209 



Turning next to animals, it may first be observed 

 that climatic conditions do not appear to exercise 

 an influence either so general or so considerable 

 as in the case of plants. Nevertheless, although 

 these influences are relatively more effective in the 

 vegetable kingdom than they are in the animal, 

 absolutely considered they are of high generality and 

 great importance even in the latter. But as this 

 fact is so well recognized by all zoologists, it will 

 be needless to give more than a very few illustrations. 

 Indeed, throughout this discussion on climatic in- 

 fluences my aim is merely to give the general reader 

 some idea of their importance in regard to system- 

 atic natural history ; and, therefore, such particular 

 cases as are mentioned are selected only as samples 

 of whole groups of cases more or less similar. 



With regard to animals, then, we may best begin 

 by noticing that, just as in the case of plants, there is 

 good evidence of the same external causes producing 

 the same effects in multitudes of species belonging 

 to different genera, families, orders, and even classes. 

 Moreover, we are not without similarly good evidence 

 of degrees of specific change taking place in correlation 

 with degrees of climatic change, so that we may 

 frequently trace a gradual progress of the former as 

 we advance, say, from one part of a large continent 

 to another. Instances of these correlations are 

 not indeed so numerous in the animal kingdom as 

 they are in the vegetable. Nevertheless they are 

 amply sufficient for our present purposes. 



For example, Mr. Allen has studied in detail 



introductory chapter, and which deal in more detail with this subject, 

 especially as regards the facies of desert floras. 



II. P 



