26 CLASSIFICATION OP FISHES. 



550. The classification of Fishes most generally received is 

 that of Cuvier, who made this group his peculiar study. It is 

 founded upon the condition of the skeleton, and upon the struc- 

 ture and arrangement of the fins. The first division of the class 

 is into the Osseous and Cartilaginous Fishes ; and this division 

 has reference, not merely to the quantity of earthy matter in the 

 skeleton, but to the number of pieces of which the jaws are 

 composed. Although the Osseous Fishes are in many respects 

 the most elevated in the scale, and have the most elaborately- 

 constructed mouth, yet many of the Cartilaginous Fishes surpass 

 them in the development of the cerebral hemispheres, which is 

 probably to be regarded as a measure of their comparative intel- 

 ligence (ANIM. PHYSIOL. 452) ; and we find in many of the 

 latter group, also, a curious modification of the reproductive 

 apparatus, which enables the young animal to derive continued 

 assistance from its parent. Yet it is in this group, also, 

 that we find the very lowest members of the class, in which 

 the vertebrated structure is almost completely lost sight of 

 ( 519). Thus we may regard the Osseous and Cartilaginous 

 Fishes as forming two parallel series, neither of which can be 

 regarded as above or below the other. Both are connected with 

 the class of Reptiles by some very curious links. 



55 1 . The sub-class of Osseous Fishes is divided in the first 

 instance into the groups ACANTHOPTERYGII, or spiny-finned, and 

 MALACOPTEBYGII, or soft-finned^ Fishes. In the former, the 

 first portion of the dorsal, or the first dorsal fin (when there are 

 two) always have spinous rays ( 523) ; of which there are also 

 some in the anal, and at least one in each ventral. In the latter, 

 all the rays, with the occasional exception of the first dorsal or 

 the pectorals, are soft or jointed. The Acanthopterygii cannot 

 be easily again subdivided, except into families ; but the Mala- 

 copterygii may be divided into three orders, according to the 

 position of the ventral fins. If these are situated under the 

 abdomen, the fishes are Abdominal ; if attached to the shoulder, 

 they are Sub-brachial ; and if wanting, they are Apodal. Each 

 of these orders, especially the first, contains numerous families. 



552. The sub-class of Cartilaginous Fishes is primarily 



