OCR Text |
Show 94 PISCES. of the branchire, and even on bones behind these arches, attached like them to the hyoides, called pharyngeal bones. The varieties of these combinations, as well as those of the form of the teeth placed at each point, are innumerable. Besides the apparatus of the branchial arches, the hyoid bone is furnished on each side with rays which support the branchial membrane. A sort of lid composed of three bony pieces, the operculum, the suboperculum, and the interoperculum, unites with this membrane in closing the great opening of the gil1s; it is articulated with the tympanal bone, and plays on one called the preopercnlum. In many of the Chondropterygii this apparatus is wanting. The stomach and intestines differ in size, figure, thickness and circumvolutions, as greatly as in the other classes. The pancreas, except in the Chondropterygii, is replaced either by c::ccums of a peculiar tissue situated round the pylorus, or by the tissue itself applied to the beginning of the intestine. The kidneys are situated along the sides of the spine, but the bladder is above the rectum, and opens behind the anus and behind the orifice of generation; exactly the inverse of what we find in the Mammalia. The testes are two enormous glands commonly termed milts; and the ovaries, two sacs about the same form and size, in whose internal folds are deposited the eggs. Some fishes copulate and are viviparous; the young fry are hatched in the ovary and issue through a very short canal. The Selachians alone, besides the ovary, have long oviducts which frequently open into a true matrix, and they produce either living ones or eggs enveloped with a horny substance. In most Fishes, however, copulation does not take place, the female depositing her ova, and the male impregnating them after extrusion. Of all the classes of animals, that of ·fishes is the most diffi· cult to sub-divide into orders from fixed and sensible charac· ters. ~fter many attempts, I have decided upon adopting the followmg arrangement, which, though it militates in some in· stan?es against precision, does not separate natural families. Fishes form two distinct series, that of FISHEs, properly PISCf~S. 95 so styled, and that of the CHONDROPTERYGII, otherwise called CARTILAGINOUS FISHES. The general character of the latter consists in the absenc of the bones of the. upper jaw, whose place is supplied by thos: of the palate ; their whole structure also exhibits evident analogies which we will describe : it is divided into three orders. The CYCLOSTOMI, whose jaws are soldered in an immovable ring, with branchial openings. The SELACHII, which have the branchire of the Cyclostomi but not their jaws. The STURIONES, whose branchial opening is the usual fissure furnished with an operculum. The ot?er seri~s: ?r t?at of the ORDINARY FISHEs, presents a prim~ry diVISIOn In those where the maxillary bone and the palatme arch are fixed to the cranium : they constitute an order which I call that of the PLECTOGN A THI and are divided into two families: the GvMNODONTES and the ScLERODERMI. I next find fishes with perfect jaws, but whose branchire instead of being pectiniform, resemble a series of small tufts: they also constitute an order which I call LoPHOBRANCHII' that comprises but a single family. ' There then remains an immense number of fishes to which no other characters can be applied than those of the external organs of motion. After much long, and laborious research, I have found that the least objectionable of these characters is the one employed by Ray and Artedi, drawn from the nature of the first rays of the dorsal and anal fin. Thus the ordinary fishes are ~ivided into MALACOPTERYGII, where an the rays are soft, With the occasional exception of the first of the dorsal or of the pectorals, and into AcANTHOPTERYGII in which the first portion of the dorsal, or of the first do;sal where there are two, is always supported by spinous rays, and where som~ of the same are always found in the anal fin, and at least one m each of the ventrals. ' ~he first may be divided by a reference to the position of their ventral fins, which are sometimes situated behind the \ |