RANK AMONG THE VERTEBRATA. 7 



that great and primary division of vertebrated animals 

 which are distinguished by their cold blood, in oppo- 

 sition to the two classes of quadrupeds and birds, which 

 have their blood warm. In all cold-blooded Vertebrata, 

 the body is either naked — that is, merely covered by a 

 skin more or less thick — or it is protected by osseous 

 pieces or plates : in some, these plates are excessively 

 hardj and are joined together at their edges, as in tor- 

 toises, and in some few of the aberrant fishes ; but in 

 the majority, both of the fishes and reptiles, the plates 

 assume that form denominated scales, the outer edge of 

 one reposing upon the base of the next. 



(6.) The rank of the monocardian classes in the 

 circle of the Vertebrata has already been touched upon.* 

 All naturalists, both ancient and modern, agree in con- 

 sidering them — what, indeed, is self-evident — as the 

 most imperfect or least organised of vertebrated animals ; 

 from the types of which, as seen in quadrupeds and birds, 

 they are at once distinguished by their cold blood, — a 

 character which is perfectly absolute, inasmuch as no 

 exception has been yet discovered : for no quadruped or 

 bird, now in existence, has any other than warm blood. 

 M. de Blainville, we believe, was the first naturalist who 

 absolutely arranged the Amphibia, or frogs, as a distinct 

 class from the true reptiles. And although this im- 

 provement on the old method has not been adopted in 

 the Regne Animal, it has generally been followed by 

 subsequent naturalists. Indeed, the very circumstance 

 of the amphibians, as Cuvier himself says, passing from 

 the form of a fish respiring with gills, to that of a rep- 

 tile respiring by lungs, is quite sufficient to separate 

 them both from fish and serpents ; since this very struc- 

 ture points them out as forming a link by which the 

 two are connected. The scientific world, however, have 

 long made up their minds on this question ; and we thus 

 find the aberrant division of the vertebrated animals 

 resolvable into three others, namely, 1. Pisces, or fishes ; 

 2. Amphibia, or frogs ; and, 3. Reptilia, or serpents. 



* Classif. of Quadrupeds, p. 45. Classif. of Animals, p 201 



B 4 



