6 THE FISH. 



but the bladder is above the rectum, and opens behind 

 the anus and behind the parts of generation contrary 

 to what occurs in the mammalia. 



The testicles are two enormous glands, commonly 

 called the soft roe or milt, and the ovaries are two 

 sacs nearly corresponding to the roe in form and size, 

 and in the internal folds of which the ova are depo- 

 sited. Some fish are capable of copulation, and are 

 viviparous ; their young break forth in the ovary 

 itself, and are born through a very short canal. The 

 selacians alone have besides an ovary, long oviducts, 

 which sometimes lead into a true matrix, and they 

 produce either their young alive, or eggs enveloped 

 in a corneous substance : but most fish do not couple ; 

 and when the female has deposited her spawn, the 

 male passes over and fecundates it by deposition of 

 the milt. 



There is more difficulty in dividing the fish than 

 either of the other classes, into orders founded on 

 fixed and obvious characters. After many trials I 

 have determined on the following distribution, which 

 in some instances is wanting in precision, but which 

 possesses the advantage of keeping the natural fami- 

 lies entire. 



Fish form two distinct series, that of fish, properly 

 so called, and that of chondropterygii or cartila- 

 ginous fish. 



The general character of the latter is, that the 

 palatine bones occupy the place of the bones of the 

 upper jaw ; the whole of the structure of these fish 



