CETACEA. 429 



a s\\'iimiiing-biadder, an organ which is so useful 

 to fishes. 



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 answers 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 of the spi- 

 racle, or orifice of the nostrils, which is placed 

 there, to the surface of the water.* 



Another peculiarity of conformation, in which 

 the cetacea differ from fishes, and which has also 

 an obvious relation to their peculiar mode of breath- 

 ing, is in the form of the tail, which, instead of 

 being compressed laterally, and inflected from side 

 to side, as in fishes, is flattened horizontally, and 

 strikes the water in a vertical direction ; thereby 

 giving the body a powerful impulsion, either towards 

 the surface, when the animal is constrained to rise, 

 or downwards, when, by diving, it hastens to escape 

 from danger. 



All the essential and permanent parts of the 

 skeleton of vertebrated animals, that is, the spinal 

 column, and its immediate dependencies, the skull, 

 the caudal prolongation, and the ribs, are found in 

 that of the Cetacea. The thorax is carried very 

 much forwards, especially in the whale, and the 

 neck is so short as to be scarcely recognisable ; for 



* The substance called Spermaceti is lodged in cells, formed of 

 a cartilaginous material, situated on tlie upper part of tiie head of 

 the Cachulot. 



