152 CLASSIFICATION OF FISHES. 



contained in the order before us are very few, our ma- 

 terials for comparison are as 1 to 10 less numerous ; 

 and yet_, upon study and reflection^ we shall find that 

 the same train of analogies can be traced^ although, 

 perhaps, they may appear to some less perfect than in 

 the instances already explained. But to proceed : — 



(133.) It will be seen that the genus Polyodon, which 

 represents a family^ stands opposite to the Chondropte- 

 ryges, or cartilaginous order. We place this genus close 

 to the sharks ; M. Cuvier does the same ; and, therefore, 

 the scruples of those who form their opinions on previous 

 authority will not be disturbed. But it may be im- 

 mediately asked^ how can Polyodon, which departs in 

 so many points from the cartilaginous structure, be, at 

 the same time, a typical representation of that order ? 

 To answer this, we shall cite an accidental remark of 

 M. Cuvier's, which, in our opinion, at least, is quite 

 conclusive. In speaking of the Polyodon, he remarks, 

 that the spinal column merely consists of one entire 

 piece, like the lamprey. Now, as one of the greatest 

 characteristics of the order before us is to have the 

 spinal column cartilaginous^ and less developed than in 

 any other order, so it results, that the most imperfect 

 fish, in this respect, among the whole of the known 

 Chondropteryges, is the Polyodon, which thus represents 

 them in its own circle. Did this peculiar construction 

 constitute the only character of the order, then, indeed, 

 Polyodon would stand at the head, and occupy that sta- 

 tion we have given to the rays : but this is not the 

 case, either in nature or in any system. Polyodon 

 has an enormous gill-cover, with a large branchial aper- 

 ture, nearly similar to the generality of fishes ; it is, 

 besides, furnished with an air-bladder j and thus nearly all 

 other parts of its structure are directly opposed to the 

 idea of placing it at the head of the cartilaginous fishes, 

 merely on the strength of having one of their characters 

 uncommonly developed : thus, also, we see that every 

 fact regarding the anatomy of an animal, however bare 

 and barren it may appear, at first, of ulterior interest. 



