president's address. 9 



many new types of life ; 3. A high increase of temperature, giving 

 tropical conditions of climate, and we have a rapid multiplication 

 of new forms and a maximum of differentiation. Again, given : i. 

 A long-continued continuity of land surface, and we have an essen- 

 tial identity of fauna ; 2. A divergence and partial isolation of land- 

 areas, and we find a moderate but decided differentiation of faunae ; 

 3. A total isolation of land-areas, and we have a thorough and rad- 

 ical differentiation of faunae, proportioned to the length of time the 

 isolation has continued. Hence, the present diversity of life is cor- 

 related with two fundamental conditions: i. Continuity or isola- 

 tion, past as well as present, of land surface ; and, 2. Climatic con- 

 ditions, as determined mainly by temperature." 



Without further comment, we will proceed to the consideration 

 (i) of the several regions concerning which there is proximate 

 agreement, and (2) next to those in dispute. 



THE NORTH AMERICAN TEMPERATE REALM OR NEARCTIC REGION. 



It is with its widest limits that this territory has been admitted 

 by Mr. Wallace, while by Mr. Allen it is deprived of the Arctic 

 region, which has been associated with the isothermal portion of the 

 Eurasia to constitute together an Arctic realm. This will be the 

 subject of consideration hereafter. Issue has also been joined as 

 to the southern limits of the realm and as to the pertinence or non- 

 pertinence to it of the Sonoran and Lower Californian "regions" 

 of Cope, but this is a question of detail which need not detain us 

 at the present time. 



THE EUROP^O-ASIATIC OR PALy^ARCTIC REALM. 



The only serious point at issue between Messrs. Wallace and 

 Allen affecting this realm is whether the Arctic portion is, or is 

 not, an integer, Mr. Wallace including it and Mr. Allen excluding 

 and uniting it with the American Arctic, and considering the two 

 as the components of a " realm," as will be hereafter seen. 



It will be now in order to inquire into the tenability of the other 

 realms whose adoption has been urged by Mr. Allen. These are 



