32 MAMMALIA. 



oily fat. Tlieir blood is warm. Their cerebral hemispheres are 

 highly developed, and folded in numerous circumvolutions. 



Such are the principal characteristic features of the Mammalia 

 which compose the order of Cetacea. 



The largest of other animals are small when compared with 

 many of the Cetacea ; these colossal creatures, however, swim 

 with more or less rapidity. In consequence of the air contained 

 in their chest, the great quantitj^ of grease with which their tissues 

 are charged, and the vigour of their caudal flukes, they move 

 easily through the waves, looking with voracity for fish, molluscs, 

 and Crustacea, of which they consume an enormous quantity. 



Whaling for these great Cetacea involves very important 

 nautical expeditions, and furnishes the raw material for the manu- 

 facture of animal oils, elastic fibres, and some ivory. 



This order is divided into two principal families, which are 

 distinguished by the food they eat^ by their teeth, and, above aU, 

 by the position of their nostrils. These are the ordinary or blowing 

 Cetacea and the herbivorous Cetacea. These two families comprise 

 a very great number of species, nearly all of which are marine.* 



Family of Blovs'ing, or Spouttng Cetacea. — The blowing 

 Cetacea have their nostrils pierced on the upper surface of the 

 head, and their nasal cavities present a peculiar arrangement, which 

 allows these animals to appear to throw up a column of water above 

 their head. The narrow opening of the blowing Cetacea has 

 received the name of spiracle or blow-hole. Their mammae are 

 placed near the termination of their bodies. Their teeth, when 

 they have any, are pointed ; but in some cases the teeth are 

 replaced by a very jDeculiar apparatus, of which we shall speak 

 presently. These animals are carnivorous. 



The famil}' of blowing Cetacea, or ordinary Cetacea, is divided 

 into two tribes, which are easily distinguished by the relative size 

 of the head: the tribe of Whales (Bakeiia), in which the head 

 constitutes in itself one-fourth or even one-third of the total 

 length of the creature, and that of the Dolpihins, in which the 

 head is in the usual proportion to the body. 



* Professor Owen has shown that the so-called herbivorous Cetacea are more 

 nearly related hy true affinity to the order Fac.htjdcnniita, and most naturalists now 

 reg-ard them as constituting a peculiar order, which was named Si/rmia hy the late 

 Professor de Plain ville. — Ed. 



