46 COMPARATIVE ANATOMY 



is the progress of the order generally, that they 

 not inappropriately have been denominated the 

 birds of the sea. The fins again are generally 

 stretched out in a horizontal position; and their 

 chief application seems to be the balancing the 

 animal ; as the moment life is extinct it falls over 

 upon its back. They appear also to be used in 

 bearing off their young, and in turning and giving 

 a direction to the velocity produced by the tail. 



But not only must the Cetacea regularly resort to 

 the surface ; it is a fact that they also descend into 

 the unfathomable depths of the ocean, and then be- 

 come exposed to a pressure which it is not easy to 

 conceive, but which forces water through the pores 

 of the hardest wood, so as to make it ever after- 

 wards sink like lead in the abyss. Whales, there- 

 fore, must be prepared to resist this pressure ; and 

 the integuments, though soft and flexible like the 

 finest velvet, are so curiously constructed as to 

 enable them effectually to do so. These, as in 

 most other animals, are composed of three parts ; 

 1st, Of the epidermis or scarf-skin, which in addi- 

 tion to its great smoothness, is remarkable for being 

 covered with a mucous oily fluid, which exudes 

 from the whole surface, though in a manner diffe- 

 rent from what we observe in fishes, which renders 

 it remarkably slippery, and opposes every thing 

 like maceration in water; 2dly, Of the rete mu- 

 cosuniy as it is called, which confers colour on 

 the negroe and in all races of man, and also dis- 

 tinctly m the whale tribe. Then succeeds, 3dly, ac- 



