162 Apodal Fishes of Bengal. 



been justly regarded as bearing a very near approximation 

 to serpents. 



The fin-rays in this order, particularly those of the dorsal 

 and anal fins, are generally composed of a single piece, 

 neither jointed nor branched, but shaped like the bony 

 spines of other fishes, from which they differ in always being 

 soft, nevertheless the rays of the caudal fin when present, 

 are frequently finely jointed and a little branched, as well as 

 those of the pectorals. 



2. Branchial Apertures. — These organs which are con- 

 stant throughout the class, are subject to many peculiarities. 

 In cartilaginous fishes, they consist of several simple trans- 

 verse fissures on each side. In fishes possessed of a bony 

 skeleton, there is a single aperture on either side, and this is 

 usually furnished with a bony frame- work, consisting of a pos- 

 terior jamb which is fixed to, or forms a part of the bones 

 of the shoulder, and a lid, consisting generally of one or 

 more thin bony plates called opercula, which are connected 

 by means of a hinge-like joint to the bones of the head. 

 This apparatus peculiar to fishes, is highly characteristic 

 of them, since there is nothing like it in any other class of 

 animals. 



In the order now under review, the branchial apertures 

 have lost the posterior jamb, as well as the bony plates form- 

 ing the operculum, and these parts where they do exist at all 

 in this order, are found to do so only in a minute rudimental 

 form. The branchial apertures in Apodal fishes are therefore 

 soft and contracted, and in some, they are both united in a 

 single opening, of which there is no example in any other 

 order. 



S. Branchial Rays. — The rays supporting a membran- 

 ous valve situated beneath the operculum, called the bran- 

 chial, or branchiostegal rays, are peculiar to fishes having 

 a bony skeleton. They undergo a great many singular 

 changes in the order now under review. In some they 



