THE FAUNAL AFFINITIES OF THE PRAIRIE 

 REGION OF CENTRAL NORTH 

 AMERICA 



DR. ALEXANDER G. RUTHVEN 

 University Miskum. Cxiykrsity of Michigan 



Those who are acquainted with the literature of the 

 field zoology of North America are familiar with the 

 fact, that, from the time of the Pacific Railroad surveys, 

 naturalists have noted that there are in North America 

 several well-defined biological regions. These have been 

 pointed out at various times by Allen, Cope, Merriam 

 and others, and the fauna of each lias been 7iiore or less 

 investigated. Of late years there has been a tendency 

 among biologists to discredit this kind of work, owing to 

 the apparent tendency of some naturalists to consider 

 the mapping of these regions as an end in itself, but it 

 seems to me that this work, if done properly, has a very 

 real value. 



If it is true that the formation of species among verte- 

 brates is orthogenetiq, as Whitman (1907) holds for 

 pigeons, and I have found to be true in the garter-snakes 

 (Ruthven, 1908), and these species are associated with 

 different sets of environmental conditions, as seems to 

 be the case, for example, in the genera Leptinotarsa 

 (Tower, 1906) and Thamnophis (Ruthven, 1908), it is 

 manifestly of importance that these areas of character- 

 ization be determined. Certain it is that the areas of 

 characterization will not be the same for all animals, for 

 the reaction of any form to anv set of environmental 

 conditions depends* fundamentally upon the constitution 

 of the animal, and this is a variable. On the other hand, 

 in the ease of terrestrial vertebrates, there would seem 

 to be enough similarity in their mode of life to render 

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