454 MANUAL OF ZOOLOGY SECT. 



dart through the water with lightning-like rapidity. By 

 lying in wait motionless, sometimes completely submerged 

 with the exception of the extremity of the snout bearing 

 the nostrils, they are often able by the suddenness and 

 swiftness of their onset to seize the most watchful and timid 

 animals. In the majority of cases the greater part, and in 

 some the whole, of their food consists of Fishes ; but all the 

 larger and more powerful kinds prey also on Birds and 

 Mammals of all kinds, which they seize unawares when they 

 come down to drink or attempt to cross the stream. 

 On land their movements are comparatively slow and 

 awkward, and they are correspondingly more timid and 

 helpless. 



The Crocodilia are all oviparous, and the eggs, as large in 

 some species as those of a Goose, are brought forth in great 

 numbers (sometimes 100 or more), and are either buried in 

 the sand or deposited in rough nests. 



CLASS V. AVES. 



In many respects Birds are the most highly specialised of 

 Craniata. As a class they are adapted for aerial life, and 

 almost every part of their organisation is modified in 

 accordance with the unusual environment. The non- 

 conducting covering of feathers ; the modification of the 

 fore-limbs as wings, of the sternum and shoulder-girdle to 

 serve as origins of the wing muscles, and of the pelvic girdle 

 and hind-limbs to enable them to support the entire weight 

 of the body on land ; the perfection of the respiratory system, 

 producing a higher temperature than in any other animals ; 

 all these peculiarities are of the nature of adaptations to 

 flight 



The Common or Domestic Pigeon is known under many 



