ORDEE OF CETACBA. 



The Cetacea are essentially aquatic animals, externally resem- 

 bling Fishes, but belonging really, by their whole structure, to the 

 class of Mammalia. They would indeed be strange Fishes, these 

 creatures, which have mammas with which to suckle their youn"-, 

 which breathe not by gills, but by lungs, and which have a heart 

 provided with two ventricles and two auricles. 



The Cetacea, then, are Mammalia. Onlj^, instead of being 

 organized for living on land, they are admirably suited for the 

 water ; some of them acquire enormous dimensions, and are the 

 giants of the animal kingdom. 



Their bod}^, more or less spindle-shajsed, is terminated behind in 

 a tail, which becomes so broad as to form a fin ; this fin is trans- 

 versal, not vortical as in fishes. The tail is the principal agent in 

 moving these living masses. 



On the back of most of the Cetacea there exists another fin, 

 which is mercl}' a modification of the skin. 



The Cetacea have no posterior members. Their anterior 

 members are transformed into natatory paddles, which are of com- 

 paratively little use for locomotion through the water, and of 

 which the principal use, no doubt, is to balance their movements. 

 These anterior members, thus changed into flippers, present, essen- 

 tially, the same structure as does the corresponding member in 

 other Mammalia — the paw of the Dog, the wing of the Bat, &c. 

 Their nostrils open, in general, from the upper part of the head. 

 Owing to this position of the nostrils, which are placed higher 

 than the mouth, these animals can breathe the air without coming 

 too much out of the water. These same organs play still another 

 part, which we will describe j)resently. 



The skin of Cetacea is generally quite hairless, which very rarely 

 happens in the case of other Mammalia. Their teeth are mostly 

 conical, imiform, and sometimes numerous. All their tissues, but 

 especially their sub-cutaneous cellular tissue, are impregnated with 



