AMERICAN ZOOLOGISTS AND EVOLUTION. 9 



his work ranks among the most important contributions to this sci- 

 ence. Mr. Allen finds that there are marked geographical variations 

 in mammals and. birds. He shows that northern mammals of the 

 same species are more thickly and softly furred, and that toward the 

 south the peripheral parts, such as the ears and feet, are more devel- 

 oped. The same law holds good in birds, a diminution in size being 

 observed toward the south, and the individuals being darker in color. 



As one goes south he meets with the same species of birds, whose 

 bodies are shorter, but whose beak, tail, and claws, are longer. On 

 the Plains, also, he found the birds with plainer tints, while south- 

 ward the colors became more intense. On drawing up a table indi- 

 cating the regions of lighter varieties, and comparing it with a chart 

 of mean annual rainfall, Mr. Allen found the lighter forms occurred 

 in dry regions, and the dark forms in relatively humid regions. To 

 sum up : Mr. Allen finds in latitudinal variation climatic influences 

 affecting color as well as altering the size of bill, claw, and tail, while 

 longitudinal variation usually affects color alone. 



He states that these laws are now so well known that a species 

 may be predicted to assume a given color if under certain specific 

 climatic conditions. 



Mr. Robert Ridgway ' has in a similar way called attention to the 

 relation between color and geographical distribution in birds as ex- 

 hibited in melanism and hyperchromatism, and has shown that red 

 areas " spread " or enlarge their field in proportion as we trace cer- 

 tain species to the Pacific coast, and that in the same proportion yel- 

 low often intensifies in tint. 



The results of these investigations can be easily understood. 

 Nearly if not quite one hundred and fifty species of birds, which 

 were recognized as distinct, are at once reduced to varieties, though 

 less than twelve years ago they were looked upon as good species, 

 with which no external influence had anything to do. Nearly if not 

 quite a fifth of the number of species of birds have been reduced by 

 the investigations of Baird, Allen, Coues, and Ridgway. 



The mammals, through the same study of geographical variation, 

 will have been reduced at least one-fourth. Already Mr. Allen 2 

 has studied the geographical variation of the squirrels, and the 

 result is that a reduction has been made of one-half the number 

 of species before recognized. Prof. Baird, in his monograph of 

 North American squirrels, reduced the number from twenty-four, as 

 acknowledged by Audubon and Bachman, to ten well-established 

 species and two doubtful varieties. Allen, with still greater advantage 

 in the shape of a mass of material from the Western surveys, l-educed 

 the ten species to five species, with seven geographical varieties. 



1 American Journal of Science and Arts, vol, iv., December, 1872, p. 454, and vol. v., 

 p. 39. 



2 " Proceedings of the Boston Society of Natural History," vol. xiv., p. 276. 



