DISTRIBUTION OF ORGANISMS. 171 



over the earth, but chiefly in warm climates, and, being for 

 the most part disliked by man, they are usually seen to decline 

 as the human population advances. Of the three great rep- 

 tilian orders, they may be considered the most carnivorous 

 and destructive, though few are of great strength. In the 

 time of the secondary formation, it was different. Vast sau- 

 rians then traversed both sea and land, the undoubted 

 masters of the animal world. Now, excepting in the croco- 

 dile family, and a few of the serpents, bulk and strength have 

 alike departed from the order. 



The Crocodilia form a distinct and well marked family, 

 comprehending the several genera of the common Crocodile, 

 distributed in Africa, India, and America, the Alligators and 

 Caimans of North America, and the Gavial, peculiar to India. 

 All of these are well known to be animals of large size, living 

 in rivers, fierce and carnivorous, and serving a useful end in 

 devouring the dead animals which are usually floated in great 

 quantities down the large continental streams. Their exterior 

 presents " distinct series of bones of moderate size, embedded, 

 as it were, in the substance of the skin, and covered externally 

 with a thick cuticle ;" hence the term loricata, or mailed, 

 which has been applied to them. The head is large, with an 

 enormous gape, and some arrangements in respect of teeth, 

 nostrils, and gullet, which appear admirably adapted for an 

 animal requiring to catch its prey in the water. The origin 

 of this reptilian family is to be sought amongst the great 

 aquatic saurians of the secondary formation ; the ichthyosaur, 

 in particular, whose head is entirely crocodilian, while its 

 general organization is fish-like. Afterwards, connecting 

 links occur in the teleosaur, steneosaur, &c. 



The remainder of the sauria present various forms tolerably 

 distinguished from each other, but which are usually compre- 

 hended under the general term lacertine, the lizard being 

 regarded as their type. First, and nearest to the crocodiles, 

 may be cited the Varanidce, a group composed of the Ouran 

 or varan of the Nile, the Monitors of both worlds, the tupi- 

 nambis, and other genera; animals living upon small reptiles 

 and insects, chiefly frequenting land, but also occasionally 



