34 Vertebrata. 



Ceratodus, of the rivers of Queensland. In several 

 respects these fishes present characteristics which are 

 identical with the embryonic conditions of many of 

 the higher groups of animals. The characters of the 

 skeleton can be seen in fig. 7. 



CHAPTER VI. 



CLASS 2, AMPHIBIA. 



19. Characters of Amphibia.^-The class Am- 

 phibia, to which we are structurally conducted by the 

 last order of fishes, consists of cold-blooded animals, 

 usually of small size. This is at present the poorest 

 in species of all the classes of vertebrata, yet, as in the 

 case of the ganoid fishes, at earlier periods in the 

 world's history the animals of this class vastly ex- 

 ceeded their present representatives in number, size, 

 and complexity. Like fishes, they are characterised 

 by having a feeble development of the outer skin, 

 or epidermis, but, unlike them, they have no dermal 

 clothing of scales, and the surface is generally smooth, 

 naked, and often glandular. Some of them, in the 

 embryonic or tadpole stage of their existence, possess 

 rudiments of the system of sense organs, like those 

 of the lateral line in fishes, but none of them are 

 retained in the adult state. Amphibians, moreover, 

 have no functional fin-rays, though sometimes they 

 have marginal membranous fringes, as in the common 

 newt or tadpole, and even rudimentary rays, as in the 



