xv GENERAL CHARACTERS 211 



absolutely helpless ; but they have to rise very frequently to 

 the surface for the purpose of respiration. They are all pre- 

 daceous, subsisting on living animal food of some kind. The 

 members of one genus alone (Oreo) eat other warm-blooded 

 animals, as seals and even animals of their own order, both 

 large and small. Some feed on fish, others on small floating 

 Crustacea, pteropods, and medusae, while the staple food of many 

 is constituted of the various species of Cephalopods, chiefly 

 Loligo and other Teuthidce, which must abound in some seas in 

 vast numbers, as they form almost the entire support of some 

 of the largest members of the order. The Cetacea are, with 

 some exceptions, timid, inoffensive animals. They are active in 

 their movements, and sociable and gregarious in their habits. 



Among the existing members of the order there are two 

 very distinct types the toothed whales, or Odontoceti, and 

 the baleen whales, or Mystacoceti, which present throughout 

 their organisation most markedly distinct structural characters, 

 and have in the existing state of nature no transitional forms. 

 The extinct Zeuglodon, so far as its characters are known, 

 does not fall into either of these groups as now constituted, 

 but is in some respects intermediate, and in others more 

 resembles the generalised mammalian type. 



The important and interesting problems of the origin of 

 the Cetacea and their relations to other forms of life are at 

 present involved in the greatest obscurity. They present no 

 more signs of affinity with any of the lower classes of 

 vertebrated animals than do many of the members of their 

 own class. Indeed, in all that essentially distinguishes a 

 mammal from one of the oviparous vertebrates, whether in 

 the osseous, nervous, vascular, or reproductive systems, they 

 are as truly mammalian as any, even the highest, members of 

 the class. Any supposed signs of inferiority are, as we shall 

 see, simply modifications in adaptation to their peculiar mode 

 of life. Similar modifications are met with in another quite 

 distinct group of mammalia, the Sirenia (Dugongs and 

 Manatees), and also, though in a less complete degree, in the 

 aquatic Carnivora or seals. But these do not indicate any 

 community of origin between these groups and the Cetacea. 

 In fact, in the present state of our knowledge, the Cetacea are 



