DISTRIBUTION OF ORGANISMS. 167 



rocercal tail, and the inferior position of the mouth, complete 

 these curious and most convincing analogies. 



The Reptiles to the cold blood of the fish add a higher 

 circulatory organization, as also lungs for aerial respiration ; 

 all of them (for exceptions are only apparent) are oviparous. 

 Amidst the confusions of existing classifications, it is possible 

 to trace three leading divisions, of which the tortoise, the 

 lizard, and the frog are the several representatives, namely, 

 the Chelonia, the Sauria, and the Batrachia. Cuvier makes 

 a fourth order of the serpents ; but Merrem and other natu- 

 ralists have shown, I think successfully, that these are but a 

 reduction from the lacertine portion of the sauria. 



The CHELONIA are remarkable for the box-like case 

 in which most of them are inclosed, a peculiar deve- 

 lopment of the ribs of the animal, and which forms an 

 admirable means of passive defence. They are animals of 

 inert faculties, but great tenacity of life, and, generally 

 speaking, the most harmless of all the reptiles, many of them 

 feeding exclusively on vegetable substances. Destitute of 

 teeth, they exhibit, like the birds, only a horny armature of 

 the jaws, and even this is, in one genus, replaced by skin 

 only. 



The Chelonia are for the most part tropical animals, being 

 seldom seen beyond the 20th degree of latitude. Within 

 that range, however, the marine species are remarkable for 

 the long voyages they annually undertake, for the purpose of 

 depositing their eggs. It is also found, from our stony records, 

 that the Chelonia were much more widely diffused over the 

 earth in the ages of the oolite and tertiary than they are now. 



The marine chelonia Turtles (Chelones) demand the 

 first notice. In this group we find the largest existing speci- 

 mens of the order ; some of them reach six and even seven 

 feet in length, and weigh seven or eight hundred pounds. 

 All of them have extremities modified into paddles, for marine 

 progression, with the toes enveloped in the membrane, and a 

 very slight development of claws ; but there is a natural divi- 

 sion of the chelones in respect of habits and even of organiza- 

 tion. One sub-group, amongst which is the common Green 



