16 REPORT OF THE SECRETARY. 



ern regions and Europe and Asia. Thus the wolf, fox, ermine, and per- 

 haps the beaver extend throughout the northern hemisphere. But few 

 species are common to the nearctic and the southern neotropical realms — 

 but one mammal and no reptiles, batrachians nor fresh-water fishes ex- 

 tend into Brazil, but a number of birds are permanent residents through- 

 out both realms. Considerable variation exists in the fauna of the sev- 

 eral parts of our region, exhibiting as many as six principal subdivisions. 

 The warmer regions are much richer in birds, reptiles, and insects than 

 the cooler, as we advance northward many species disappear, while 

 a few others are added. The natural division of the eastern part of 

 the continent is in a measure dependent on the isothermal lines which 

 traverse it. In accordance with this fact, the following districts of the 

 eastern region have been proposed, viz : The Carolinian ; the Alle- 

 ghanian ; the Canadian, and the Hudsonian. The central region is 

 characterized by the general absence of forests. It presents two divis- . 

 ions, each peculiar in its vegetation ; the division of the plains which 

 extends from the eastern border to the Rocky Mountains to the 100th 

 meridian, and the Bocky Mouutain region itself, which extends to the 

 Sierra Nevada. The former is covered with grass and is almost totally ' 

 treeless ; the latter is covered with sage-brush. 



In regard to the batrachia and reptilia, from their small amount of 

 animal heat, it follows that temperature has the greatest influence on 

 their life and distribution. This is exhibited not only in multiplication 

 of forms, but in the brilliancy of color. Another important influence 

 in regard to these animals is the amount of terrestrial and atmospheric 

 moisture. A peculiarity of cold-blooded vertebrata of arid regions is 

 that hy means of which they readily assume the color of the body on 

 which they rest. That a prevalent color of such bodies should lead to 

 a habit of preference for that color is necessary, aud as such habits 

 become automatic, the permanence of the color is naturally established. 



Appended to the paper is a bibliography of works and memoirs which 

 embrace discussions of systematic or distributional relations of the rep- 

 tiles of North America. Those embracing descriptions of species only, 

 will be added in a future publication. This number forms a pamphlet 

 of 108 octavo pages, and has been distributed to the principal museums 

 and naturalists of the world. 



The second number of the Bulletin of the National Museum is an ac- 

 count of the birds of Kergueleu Island, by Dr. J. H. Kidder, Surgeon 

 United States Navy, aud edited by Dr. Elliott Coues. These specimens 

 were collected by Dr. Kidder, surgeon and naturalist of one of the 

 parties organized for observing the transit of Venus in the southern 

 hemisphere. The party to which Dr. Kidder was attached landed from 

 the United States ship Swatara at the upper end of Royal Sound, a 

 deep indentation in the southern part of Kerguelen Island, otherwise 

 known as Desolation Island, one of the most extreme islands of the 

 southern hemisphere. It is a region of almost constant precipitation, 



