414 TNTEODrCTION TO ZOOLOGY. 



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

 it is vertical (ante, p. 204) ; and the adaptation in each 

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

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

 and they may speed onwards in their com*se at nearly the 

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

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

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

 inconceivable power ; its superficial measm-ement 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 condition 

 of the body to prevent its absolute destruction. The most ob- 

 vious means for meeting this enormous pressm-e, 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 efiected 

 in a manner which must excite the greatest admiration."t 

 Professor Jacob, of Dublin,;}; has shown that the structm-e in 

 which the oil is deposited, and which is called " blubber,' ' is 

 the ti'ue skin of the animal, modified for the purpose of holding 

 this fluid oil, but still the true skin. It consists of an interlace- 

 ment of fibres, crossmg 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 thick- 

 ness 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 be- 

 tween one and two feet thick, it operates like so much 

 caoutchouc, possessing a density and resistance which the 

 more it is pressed, it resists the more." § 



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

 time. Vide Naturalist's Library, vol. vii. ; or article "Cetacea," Encyclo- 

 pedia of Anatomy and Phj-siology. 



t Bell. 



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



§ Naturalist's Library, vol. vii., quoted by licll. Above a year before we 



