MUSEUM OF COMPARATIVE ZOOLOGY. 419 



plains the occurrence of the large proportion of long-winged birds, and 

 especially of the preponderance of the water birds, in the three first 

 primary divisions given above of the birds of the Eastern Province, 

 namely, the cosmopolitan, the circumpolar, and the continental, and the 

 small proportion of such species among those restricted in their longi- 

 tudinal range to the Eastern Province. Most of the circumpolar 

 species are also boreal ones. 



II. The aquatic species, while forming only about four tenths of the 

 birds found in the Eastern Province, greatly predominate over the 

 land species in the boreal regions, in the Arctic Realm they outnum- 

 bering the land birds in the proportion of five to one, or form eight 

 tenths of the whole. In the Cold-temperate District of the North 

 American Region the water-birds form about six tenths of the whole ; 

 in the Middle-temperate Districts, between four and five tenths ; in 

 the Warm-temperate District, rather less than four tenths. Farther 

 southward, although a few groups (as the Rallidce, Herodiones, and 

 Sternince) are more numerously represented, the relative proportion 

 of water birds to the terrestrial seems scarcely to increase. In the breed- 

 ing season, however, a numerical comparison of the land and water 

 birds yields very different results, in respect to the proportion char- 

 acteristic of localities situated under different parallels of latitude. 

 Passing from the extreme boreal regions southward, the number of 

 Grcdlce (exclusive of the Paludicolce), Anatidce, Larince, and Lestrid- 

 ince decreases rapidly, so that the number of the Grallce (exclusive 

 of the rails and their allies) is reduced in the breeding season, in the 

 warm-temperate parts of the Eastern Province, to only seven or eight 

 species, the Anatidce to one (Aix sponsa), the Larince to one (C/irceco- 

 cephalus atriciUa), and the Lestridince disappear entirely. 



III. A large proportion of the accessions to the land birds near the 

 tropics being species of a comparatively low grade of structure, the 

 prevalence of the water birds in the arctic and subarctic fauna;, the 

 comparative absence of water birds in the temperate latitudes, and the 

 great development here of the higher groups of the land birds, give to 

 the temperate regions the maximum proportion of high forms of avine 

 life, — a fact as true in respect to mammalian life as it is of birds. 



IV. In respect to the distribution and relative development of par- 

 ticular families, the Sittidce (Sittce), the Paridce, and the Alcidce are alone 

 restricted to the North Temperate Realm. The species of these groups 



