DISTRIBUTION OF ORGANISMS. 193 



interstices of the osseous frame, as we advance from the marine 

 and fluviatile species. These interstices are seen in the youth 

 of the emydes and land-tortoises, but as age advances, they are 

 obliterated. But what is in them a youthful and transient 

 character, is permanent in the former animals, marking clearly 

 their precedence in the genealogical scale. 



No better word than SAUEIA seems attainable for the greatly 

 varied order which next occurs, a combination of all the loricate 

 and squamate reptiles. The crocodile, the lizard, and serpent, 

 will suggest the principal forms to those least acquainted with 

 zoology. They are extensively distributed 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 popu- 

 lation advances. Of the three great reptilian 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. Huge saurians then traversed both sea and 

 land, the undoubted masters of the animal world. Now, ex- 

 cepting in the crocodile 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, com- 

 prehending the several genera of the common Crocodile, distri- 

 buted 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 de- 

 vouring the dead animals which are usually floated in great 

 quantities down the continental streams. Their exterior pre- 

 sents " 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 enor- 

 mous gape, and some arrangements in respect of teeth, nostrils, 

 and gullet, which appear admirably adapted for an animal re- 

 quiring to catch its prey in the water. The origin of this rep- 

 tilian 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 organiza- 

 tion is fish-like. Afterwards, connecting links occur in the 

 teleosaur, steneosaur, etc. 



The remaining sauria present various forms tolerably distin- 

 guished from each other, but which are usually comprehended 

 under the general term lacertine, the lizard being regarded as 



o 



