334 THE MECHANICAL FUNCTIONS. 



the bosom of the primeval ocean, or stalked with gigantic 

 strides across antediluvian plains, and whose scattered re- 

 mains bear fearful testimony of the convulsions of a former 

 world, certain it is that, at the present day, the whales of 

 the northern seas are the most colossal of the living animal 

 structures existing on the surface of this planet. 



A cursory survey of the organization of the tribes belong- 

 ing to this semi-amphibious family, will impress us with the 

 resemblance they bear to fishes; for they present the same 

 oval outline of the body, the same compact form of the 

 trunk, which is united with the head without an intervening 

 neck; the same fin-like shape of the external instruments of 

 motion, and the same enormous expansion and prolongation 

 of the tail, which is here also, as in fishes, the chief agent in 

 progression. With all this agreement in external charac- 

 ters, their internal economy is conducted upon a totally dif- 

 ferent plan; for although constantly inhabiting the ocean, 

 their vital organs are so constructed as to admit of their 

 breathing only the air of the atmosphere, and the conse- 

 quences which flow from this difference are of great import- 

 ance. The necessity of aerial respiration compels them to 

 rise, at short intervals, to the surface of the water; and this 

 air, with which they fill their lungs in respiration, gives 

 their bodies the buoyant force that is required to facilitate 

 their ascent, and supersedes the necessity of a swimming 

 bladder, an organ which is so useful to the fish. 



With the intent of diminishing still farther their specific 

 gravity, nature has provided that a large quantity of oily 

 fluid shall be collected under the skin, a provision which an- 

 swers, also, the purpose of preserving the vital warmth of 

 the body. A great accumulation of this lighter substance is 

 formed on the upper part of the head, apparently with a view 

 to facilitate the elevation to the surface of the blowing hole, 

 or orifice of the nostrils, which is placed there.* 



Another peculiarity of conformation, in which the cetacea 



* The substance called Spermaceti is lodg-ed in cells, formed of a cartilagi- 

 nous substance, situated on the upper part of the head of the Cachalot. 



