37o CETACEA. 



sarily restricted in their growth, and their bulk is apportioned to 

 the strength of the limbs that bear their weight ; but, in the 

 water, being buoyed up on every side by the denser medium, the 

 size of aquatic animals becomes of little consequence; thus the 

 whales attain prodigious dimensions, and, from the inexhaustible 

 supply of food with which they are surrounded, find abundant 

 materials for their sustenance. 



The Cetacea are Mammals altogether deprived of hinder limbs. 

 The trunk of their body is prolonged without any line of de- 

 marcation into a thick tail, terminated by a broad fin, very much 

 resembling in its general shape that of a fish, but entirely com- 

 posed of an expansion of the skin supported by a tough cartila- 

 ginous substance, and, instead of being placed vertically, to strike 

 the water from side to side, it is horizontal, so that by means of 

 its upward and downward movements, these animals easily come 

 to the surface, or plunge perpendicularly into the depths below : 

 their head is joined to the body without the intervention of any 

 apparent neck, and their* arms, the representative of the fore 

 limbs of quadrupeds, are so flattened and concealed by the skin, 

 that they might easily be mistaken for pectoral fins. When de- 

 nuded of their flesh, however, they present, under a modified 

 shape, bones and fingers corresponding with those met with in 

 the lion or the bat. Thus, constructed entirely for swimming, 

 the Cetacea are strictly confined to the watery element ; neverthe- 

 less, they breathe air by means of lungs, and are thus perpetually 

 obliged to come to the surface for the purpose of respiration. 

 Their blood is hot ; they bring forth living young, which they feed 

 with their own milk, precisely in the same way as the terrestrial 

 quadrupeds; and thus in all the details of their structure they 

 differ widely from the cold-blooded, gill-breathing, and oviparous 

 fishes. Diving, as the whales not unfrequently do, to consider- 

 able depths, their bodies are subjected upon such occasions to 

 enormous pressure, to sustain which their body is enveloped in 

 a covering that possesses great elasticity. Their skin is greatly 

 thickened, and made up of a texture of interwoven fibres enclosing 

 an immense quantity of oil or blubber, thus forming an integu- 

 ment admirably adapted to resist compression. This thick blanket 

 of fat, moreover, retains the vital warmth, and thus enables the 

 Cetaceans even to inhabit the coldest regions of the ocean. Being 

 lighter than water, it also greatly contributes to the buoyancy of 

 these unwieldy animals. A dead whale floats ; but the carcase, 

 when stripped of the blubber, sinks immediately. 



