CABTILAGINES. GENERAL CHARACTERS. 121 



more especially as we should then cast aside all regard 

 for outward form, by which Nature, as it were, stamps 

 the most obvious and tangible affinities of her own 

 groups. The lampreys, indeed, have a second cha- 

 racter in common with the sharks and rays ; which is, 

 in having more branchial apertures than any of the 

 other eel-Uke fishes of the order Apodes : but when 

 we see, even in the same genus of sharks, that the 

 number of these orifices is by no means constant, and 

 that in the sturgeons and the chimaeras, regarded by all 

 writers as true Cartilagines, these orifices are only one 

 on each side, as in the MurtsnidcE, it becomes obvious 

 that number alone is but an inferior character, [and 

 cannot be considered as a primary distinction even of 

 a genus, much less of an order. These considerations 

 are sufficient to excite very strong doubts on the pro- 

 priety of placing Petromyzon in the present order. If 

 we look again to the relations of these two groups, 

 this opinion receives additional strength. The affinity 

 which the cartilaginous fishes bear to the aquatic order 

 of quadrupeds — that is, to the whales and the porpoises 

 — is too well known and acknowledged to be here de- 

 tailed ; while that between the lampreys and the red- 

 blooded worms is no less evident : both these affinities, 

 indeed, have been acknowledged by Cuvier ; and it 

 therefore follows as an inevitable consequence, that these 

 two groups of fishes must be kept distinct, — the car- 

 tilaginous being placed nearest to the Mammalia , while 

 the lampreys are arranged so as to form a passage to 

 the Annulosa, by means of the Annelides, or red-blooded 

 worms. Cuvier, indeed, well observes that the ^4ampreys 

 have a skeleton so defective, and such simplicity of 

 organisation, that we might almost arrange them with 

 the worms :" they are, in short, if not " the most im- 

 perfect of all vertebrated animals," at least the most 

 imperfect of the entire class of Pisces. Excluding, 

 therefore, the Cyclostomi Cuv. from this order, we find 

 that the remainder of our author's Chondropterygii form 

 a natural group ; the primary divisions of which we 



