430 INTRODUCTION TO ZOOLOGY. 



The position of the tail in Whales is horizontal; in fishes 

 it is vertical (ante, p. 220) ; and the adaptation in each 

 instance is admirahly fitted to the wants of the animal. For 

 fishes it is used as an instrument for progression in the water, 

 and they may speed onwards in their course at nearly the 

 same uniform depth. But by the very nature of their organi- 

 zation, Whales are compelled to rise to the surface for each 

 respiration;* and as the tail is horizontal, it acts as an oar of 

 inconceivable power; its superficial measurement in the larger 

 species being not less than one hundred feet. 



"But if this powerful implement be necessary to raise the 

 Whale into contact with the atmosphere, the immense depth 

 of water from which he is thus raised implies a superincumbent 

 pressure so immense as to require some extraordinary condi- 

 tion of the body to prevent its absolute destruction. The 

 most obvious means for meeting this enormous pressure, which 

 in most cases must amount to 154 atmospheres, or about a 

 ton upon every square inch, is a thickening of the integument, 

 or the production of some incompressible substance, which 

 shall invest the whole animal: and we find this object to be 

 effected in a manner which must excite the greatest admi- 

 ration, "t Professor Jacob, of Dublin, J has shown that the 

 structure in which the oil is deposited, and which is called 

 "blubber," is the true skin of the animal, modified for the 

 purpose of holding this fluid oil, but still the true skin. It 

 consists of an interlacement of fibres, crossing each other in 

 every direction, as in common skin, but more open in texture, 

 to leave room for the oil. A soft wrapper of fat, like that of 

 the Hog, would not have answered the purpose. " Though 

 double the thickness to that usually found in the Cetacea, it 

 could not have resisted the superincumbent pressure; whereas, 

 by its being a modification of the skin, always firm and elastic, 

 and in this case being never less than several inches, and 

 sometimes between one and two feet thick, it operates like so 

 much caoutchouc, possessing a density and resistance whicli 

 the more it is pressed it resists the more."g 



* Some of the larger species can remain under water for a considerable 

 time. Vide Naturalists' Library, vol. vii. or article " Cetacea," Encyclo- 

 pedia of Anatomy and Physiology. 



f Bell. 



J Dublin Philosophical Journal, i. p. 356, quoted by Bell. 



Naturalists' Library, vol. vii. quoted by Bell. Above a year before we 



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