G. NATURAL HISTORY AND ZOOLOGY. 333 



material in the National Museum at "Washington, he has oc- 

 casion to reduce the number of species still lower than that 

 allowed by Professor Baird in his monographs of the same 

 forms, finding that many of those which have hitherto been 

 considered as species are in reality merely climatic or ge- 

 ographical races, several of which are referable to a common 

 type. 



A striking generalization obtained in his investigations 

 has reference to the increasing intensity of color of the spe- 

 cies in proceeding from the north southward, this being very 

 evident in the fox-squirrel of the Mississippi Basin, the belly 

 of which in the northern part of its range is almost white, 

 while in specimens from Lower Louisiana it is reddish-fulvous, 

 or a deep orange. Equally decided differences exist in spec- 

 imens of the same species as they proceed from east to west. 



Mr. Allen now considers that we have at least five more or 

 less w T ell-marked areas characterized by certain peculiarities 

 of color variation in mammals and birds, as well as by a close 

 relation between the areas, the prevalent tendencies of change 

 of color, and the amount of aqueous precipitation. The first 

 of these regions is that of the Atlantic slope, which includes 

 not only the country east of the Alleghanies, but a large 

 part of the British possessions, extending westward as far as 

 Fort Simpson, and northward and westward to Alaska, in- 

 cluding, apparently, all that territory north of the Alaskan 

 Mountains, and having an annual rain-fall of about thirty- 

 five to forty-five inches. This region, in view of its great 

 extent, he selects as representing the average or normal type 

 of color, the variation in other regions being in the direction 

 of intensity. 



The second region embraces the Mississippi Valley, or, 

 more properly, the Mississippi Basin, and is termed the Mis- 

 sissippi Region. Here the annual rain-fall reaches forty-five 

 to fifty-five inches, and sometimes more. In this region the 

 tendency is to an increase of fulvous and rufous tints, these 

 reaching their maximum in the limited area of greatest 

 humidity, although a general increase of color is more or less 

 characteristic of the region. 



The central portion of the Rocky Mountains forms the 

 third region, to be called the Colorado Region, as including 

 the greater part of that territory within its limits. Here 



