DISTRIBUTION OF ORGANISMS. 189 



three advances made to its lower confines from the inverte- 

 brata namely, by the cephalopodous mollusks, by the annu- 

 lose animals (annelides), and by the echinodermata. And we 

 see advances made in its upper confines to the next higher 

 class, the REPTILIA, which succeed it in the strata and 

 chronology of the earth, as in organization. 



It is also sufficiently clear, that the succession of fishes upon 

 our globe was in conformity with the embryonic development 

 of the individual fish of a high order. This has been denied ; 

 but against all inferior authorities, that of M. Agassiz must on 

 such a point be held incontestable. He expressly affirms it as 

 proved "that the embryo of a fish during its development, the 

 class of living fishes in its numerous families, and the fish type in 

 its planetary history, in every respect go through analogous 

 phases" The want of substantial vertebrae in the Devonian 

 fishes is found in the last gradation of the class of fishes, among 

 the Cyclostornes. He has reason to think that the internal 

 case for the brain in the Devonian fishes was cartilaginous. So 

 it is in the sturgeon, so it is in all embryos. Certain arrange- 

 ments of the fins, as well as the heterocercal tail, and the 

 inferior position of the mouth, complete these curious and im- 

 pressive analogies. 



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

 culatory 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 naturalists 

 contend that these are but a reduction from the lacertine por- 

 tion of the sauria. 



The CHELONIA are remarkable for the box-like case in 

 which most of them are enclosed, a peculiar development 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 jaw, 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 

 rano-e, however, the marine species are remarkable for the long 



