No. 567] EFFECT OF DISTRIBUTION ON SPECIATION 133 



of the various families of Insectivores, but as some of the 

 families have not been as intensively studied as others, 

 and as the conditions affecting their distribution and 

 speciation are so different in different families, we could 

 hardly expect accurate results, and yet the table clearly 

 shows a tendency for the families having wider ranges 

 to have a higher index of modification, the almost cosmo- 

 politan shrews, for instance, having 11.36 species per 

 genus, and the families with restricted range (Galeopi- 

 thecidae, Solenodontidae, Centetidae and Potamogalidaa), 

 having only 1 to 3 species per genus. The Talpidae and 

 Chrysochloridae do not seem to conform in their speciation 

 to what should be expected. 



When the specific and generic subdivisions of all the 

 families of mammals have been worked out more per- 

 fectly, and their ranges in a distributional sense, i. e., 

 through life zones, faunas, and associations, are more 

 accurately known, some interesting facts concerning the 

 relation between their indices of modification, and the 

 extent of their ranges, might be brought out. 



It is interesting to note that there is a considerable 

 number of conspicuous examples of wide-ranging genera 

 which are remarkably poor in species. Among carnivo- 

 rous mammals there are many such cases, these animals 

 seeming to be adaptable to an almost unlimited range of 

 environmental conditions without modification, or, in 

 other words, their germ plasm is not stimulated to change 

 by altered conditions of climate or environment. The 

 tiger, for instance, is equally at home in the bleak frozen 

 steppes of Siberia, or in the hot humid jungles of India. 

 The genus Cynaelurus is widely distributed over the 

 Ethiopian and Oriental regions, and yet it contains but a 

 single species, with several geographic races. Among 

 birds there are a number of similar examples, the most 

 striking case, perhaps, being Pandion, a cosmopolitan 

 genus with but a single species. The same peculiar condi- 

 tion occurs among lower animals, as for instance in the 

 I>inofiagellate genus Diplopsalis, which is cosmopolitan 



