8 THE FISH. 



fin, and into acanthopterygii, in which the first por- 

 tion of the dorsal fin, or the first dorsal fin, when 

 there are two, is supported by spinous rays, and in 

 which the anal fin has also some of these spinous 

 rays, and the ventrals at least one each. 



The former may be subdivided without inconve- 

 nience by the position of the ventral fins, in some 

 situated behind the abdomen, in others suspended to 

 the humeral apparatus, and in the remainder absent 

 altogether. 



We thus arrive at the three orders of Malacoptery- 

 gian fish, viz. the abdominal, subbrachian, and apodal 

 fish, each of which includes some natural families, 

 which we will explain. The first especially is very 

 numerous. 



But a similar basis of division cannot be used in 

 the acanthopterygii, and the problem how to establish 

 other subdivisions than the natural families, is still 

 insoluble to me. Fortunately many of these families 

 present characters nearly as precise as those that 

 could be given to genuine orders. 



One cannot assign to the families of fish ranks so 

 determinate as to those of the mammalia. Thus the 

 chondropterygii are allied in one respect to the 

 reptiles by the organs of sense, and even by those of 

 generation in certain of them, while they hold a 

 similar alliance with the mollusca and worms, by the 

 imperfection of the skeleton, in others. 



With respect to the common fish, if any system of 

 structure is more developed in some than in others, 



