4G ESSAY ON CLASSIFICATION. 



marine and partly fluviatile ; the Eeptiles are either 

 aquatic or amphibious or terrestrial, and some of the 

 latter are aquatic during the early part of their life ; the 

 Birds are all aerial, but some more terrestrial and others 

 more aquatic ; finally, the Mammalia, though all aerial, 

 live partly in the sea, partly in fresh water, but mostly 

 on land. A more special review might show that this 

 localization, in connection with the elements in which 

 animals live, has a direct reference to peculiarities of 

 structure of such importance that a close consideration of 

 the habitat of animals, within the limits of the classes, 

 might, in most cases, lead to a very natural classification. 1 

 But this is true only within the limits of the classes, and 

 even here not absolutely, as in some the orders only, or 

 the families only, are thus closely related to the elements ; 

 and there are even natural groups, in which this connec- 

 tion is not manifested beyond the limits of the genera, and 

 a few cases in which it is actually confined to the species. 

 Yet, in every degree of these connexions we find that 

 upon every spot of the globe it extends simultaneously to 

 the representatives of different classes, and even of dif- 

 ferent branches, of the animal and vegetable kingdoms ; 

 a circumstance which shows, that, when called into exist- 

 ence in such an association, these various animals and 

 plants were respectively adapted, with ah 1 the peculiarities 



Mitchell; London, 1844-1849, 3 vols. 4to. See also the works quoted 



imp. 4to. BONAPARTE (C. L.), Con- above, Sect. 2, and the annual reports 



spectus generum Avium, Lugduni- in Wiegman's Archiv, now edited by 



Batavorum, 1850, and seq., 8vo. For Troschel ; the Catalogues of the Bri- 



that of Mammalia: WAGNER (A.), tish Museum, of the Jardin des 



Die geographische Verbreitung der Plantes, etc., furnish equally irnpor- 



Siiugthiere, Verhandl. der Akad. der tant information. 

 Wissensch. in Miinchen, vol. iv. 1 AGASSIZ (L.), The Natural Rela- 



POMPPER (HERM.), Die Saugthiere, tions between Animals and the Ele- 



Vo'gel und Aniphibien, nach ihrer ments in which they live. Amer. 



geographischen Verbreitung tabella- Jour, of Sc. and Arts, 2d ser., vol. 9, 



rish zusammengestellt; Leipzig,1841, 1850, 8vo., p. 369. 



