322 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



tention, especially of species that range across the continent. 

 This abstraction of a dusky or melanistic shade of the birds 

 tends to bring out the pattern much more distinctly, as seen 

 in the representatives in that region of the night-hawk, the 

 meadow-lark, etc. 



Most of the species of this region, heretofore supposed to 

 be distinct, Mr. Allen considers as simple races of forms found 

 in the Atlantic States. The difference in color between the 

 Pacific forms of the arid and the comparatively moist regions 

 is greater toward the end of the breeding season, or just be- 

 fore the autumnal moult, than afterward, or in spring speci- 

 mens, showing the more unmistakably the direct influence of 

 the intensely heated dry winds and strongly reflected light 

 upon the color of birds in semi-desert regions. 



Another generalization referred to by Mr. Allen is that 

 birds exhibit a greater tendency to the enlargement of the 

 bill to the southward, along the Pacific slope of the conti- 

 nent, just as there is, to perhaps a less extent, in the Atlantic 

 region. As regards color, there is a narrow belt extending 

 from the valley of the Columbia River northward along the 

 Pacific coast, where the annual rain-fall is nearly double that 

 of any other portion of the continent, and in which the birds 

 not only exhibit the brighter colors of the region east of the 

 great plains, but frequently take on a peculiar deep plumbe- 

 ous or dusky brown, accompanied by a partial obsolescence 

 of spots and streaks, especially in the FringilUdce. 



Mr. Allen takes strong ground against the idea of hybrid- 

 ity in birds, by which it has been attempted to explain the 

 occurrence of intermediate forms, linking the so-called species 

 of the different provinces of North America along or near 

 their supposed line of separation. These hybrids, according 

 to some authors, Mr. Allen considers to be expressions of the 

 same law of variation which established the primary races ; 

 and he suggests that, in passing from the Atlantic to the Pa- 

 cific, the forms will be comparatively uniform as long as the 

 physical conditions remain constant, while as these conditions 

 change more or less abruptly the effect upon the birds will 

 be more or less strongly marked. 



The observations of Mr. Allen establish the occurrence of 

 numerous eastern species at points several hundred miles to 

 the westward, and of western species considerably to the east- 



