30 



NATURAL HISTORY OF VERTEBRATE ANIMALS 



the land, but very graceful In the water. It is "tied" to the land 

 by its manner of breathing and producing young, just as the toads, 

 among Amphibia, are "tied" to the water by the necessity of a 

 moist atmosphere and by their breeding habits. 



The foregoing examples enable us to understand something of 

 the diversification in habits and habitats of the vertebrate group as 

 a whole. The oceans in all their depths, the land surface even to 

 the poles, and the air constitute the limits of distribution. No 

 other one of the large animal groups, unless it be the Arthropoda 



YiG. 16.— American fur seals at rookery, and adult male and his "harem" 

 of females. Other similar groups are seen in the background. These seals 

 come to the rookeries in summer, giving birth to the young on land. During 

 the remainder of the year they live in the open waters of the North Pacific. 



(Photo, by courtesy of the American Museum of Natural History.) 



(cf. Fig. 117, p. 240), ranges so widely. This much can be said 

 in general. To go further would necessitate detailed references to 

 individual species, some examples of which have been given in the 

 Amphibia. Of all the types of vertebrates, the human kind has 

 ranged most widely. No other single species can compare with 

 man in this particular, unless it be some of the animals associated 

 with him, such as rats and other vermin. Taken as a whole, there- 

 fore, the vertebrates show a great range of habitat. The fishes, 

 which are the simplest vertebrates, are adapted for aquatic Hfe; 



