AND COMPARATIVE ANATOMY. 47 



sea, as the whale kind, the walrus, the manati, and the seals, 

 are rendered buoyant in this dense fluid by a thick stratum 

 of fat laid over the whole body under the skin. From this, 

 which is called blubber, the whale and seal oil are extracted. 

 The object of this structure in lightening these huge crea- 

 tures, and facilitating their motions, is obviously the same 

 as that of the air-cells in birds, in relation to the element 

 they inhabit. 



A scientific acquaintance with the animal kingdom is not 

 only valuable in its immediate reference to zoology and phy- 

 siology, but it aids other sciences — affording lights whicli 

 are not merely useful, but absolutely indispensible in exa- 

 mining and illustrating other departments of natural know- 

 ledge. An exemplification occurs in geology, or the sci- 

 ence v/hich treats of the physical construction of our globe. 

 Certain rocks and earthy strata contain vast numbers of 

 shells, exuviae of zoophytes, bones and teeth of large 

 animals, besides other organic substances, in a fossile state. 



Considerable mountains and extensive districts are some- 

 times composed entirely of such animal remains. It is the 

 business of the naturalist to compare these organic remains of a 

 former world with the corresponding objects in the present 

 order of things ; to determine their resemblances or difl'er- 

 ences — whether they are of the same or of different species 

 or genera ; to compare the productions of the different strata 

 to each other, and to distinguish those which have belonged 

 to fresh, from those of salt-water animals ; and lastly, to 

 ascertain whether the organic fossils of each country are like 

 the living animals of the same, or of different and remote 

 regions and climates. Such investigations require extensive 

 and accurate information — an acquaintance, both with the 

 great outlines and minute details of nature ; and belong 

 therefore to an advanced stage of science. They have been 

 commenced with zeal and industry by some of the greatest 

 modern naturalists, and have led to highly interesting re- 

 sults. The bones of large quadrupeds found in such num- 

 bers in almost all the countries of the old and new Con- 

 tinent, have been discovered to belong to species, and even 



