154 



ICHTHYOLOGY. 



Introduc- are characterised by having their exterior margin fixed to 

 tion. ti,g skin, with as many openings for the issue of the water 

 "^ as there are intervals between the branchiae themselves ; 

 but all other fislies have the external margin of the bran- 

 chia; free, and the water which enters the mouth escapes 

 by the opening of the gill-covers. 



A certain number of the fins are vertical, and serve the 

 fish somewhat in the same way as a vessel is served by her 

 helm and keel. Of these, some, called dorsal, are attached 

 to the back, others, beneath the tail, are named anal, while 

 a fine expansion, which usually terminates the body, is 

 known as the caudal fin. All these are vertical fins, and 

 vary in different tribes, either in number, or dimensions, or 

 the nahu-e of the rays by which they are supported, and 

 which arc sometimes spiny, sometimes branched and com- 

 posed-of numerous articulations. The other fins are dis- 

 posed in pairs, and rejDrcsent the foia- external members of 

 the higher classes, such as quadrupeds and birds. Those 

 which correspond to the fore-legs of quadrupeds and the 

 wings of birds are named the pectoral fins, and are always 

 attached behind the gills ; those again which are regarded 

 as the analogues of the hinder extremities of the other 

 classes are named the ventral fins, and have a considerable 

 range of position in different species, from as far forward 

 as beneath the throat, to the origin of the tail. Like the 

 vertical fins, they also vary in size, and in the number and 

 structure of their rays ; and one or even both pairs are oc- 

 casionally wanting, as in eels, which have no ventral fins, 

 and Murena;, which have neither ventral nor pectoral fins. 

 Indeed the Apierichti have no fins at all. 



Those fishes are named Malacopterygian, of which 

 all the rays of the fins are articulated, and of a softer struc- 

 ture : while such as are characterised by Jiaving at least a 

 portion of their rays hard, simple, and in the form of spines, 

 are included under the general title of Acanthoptery- 

 GiAN fishes.' These great divisions apply solely to the os- 

 seous species. We have already mentioned that the car- 

 tilaginous kinds are distinguished by the name of Ciion- 

 DRoPTERYGiAN, while two Icsscr groups, in some respects 

 intermediate between these and the preceding, fall under 

 the orders Lophobranchii and Plectognatiii of Baron 

 Cuvier. 



The differences hitherto alluded to are connected with 

 intimate structure — with the skeleton or bony frame-work 

 of the fish. There are of course others of a slighter or 

 more superficial character. The jaws may be armed with 

 teeth of all sorts, and these weapons sometimes occupy all 

 parts of the mouth, and are found occasionally even in the 

 throat. The lips are frequently furnished with a kind of 

 fleshy beard or barbies, which differ greatly in number, size, 

 and substance. Some have long fleshy isolated filaments 

 hanging to the body, as in Scorpaiia; and occasionally one 

 or more of the rays is to a certain extent detachable from 

 the fin, and susceptible of independent movement. 



The nature of the surface or external tegument of fishes 

 also varies greatly. Some may be called naked, while 

 others are scaly, spinous, or plated, in whole or in part. 

 If to these considerations we add the infinitely varied cha- 

 racter of colour in all its admirable distributions, and the 

 differences in size and weight observable in fishes, we shall 

 be able to form a general idea of the external aspect of this 

 great and important class. 



SECT. III. THE OSTEOLOGY OF FISHES. 



In regard to the texture of the bones of fishes, their 

 skeletons are either bony, Jibro-cartilaginous, or truly car- 



tilaginous. Those distinguished by the last-named charac- 

 ter are the chondropterygian groups, such as the sturgeons, 

 sharks, and rays, all of which exhibit throughout the whole 

 of their frame-work, in their branchiae (the external bor- 

 der of which is fixed to the skin, and through which the 

 water is allowed to escape only by narrow openings), and 

 in other important parts of their organization, distinctive 

 characters, which obviously separate them from all other 

 fishes. They are in fact destitute of true bones, their har- 

 der parts consisting only of a homogeneous and semitrans- 

 parent cartilage, which is merely covered on the surface 

 in certain genera by a layer of small, opake, calcareous gra- 

 nules, closely set together. In the lampreys even this en- 

 velope is wanting, while among the Ammocates the skele- 

 ton continues in an actually membranous condition. The 

 sturgeons and Chimera; partake in some measure of the 

 lamprey character in relation to the softness of their spines, 

 but the first-named genus is possessed of many true bones 

 of the head and shoulder. 



Other fishes differ in their osteological character chief- 

 I3' in the hardness of their skeleton, and it is without rea- 

 son that the fibro-cartilaginous kinds have been associ- 

 ated by some authors with the Chondropterygii. The 

 calcareous matter, that is, the phosphate of lime, is de- 

 posited in layers and fibres in the cartilage which forms 

 the basis of their bones, precisely in the same manner 

 as among the hard-boned species, but less abundantly ; 

 and the texture of the bone never becomes so hard and 

 homogeneous as among the osseous kinds. Thus in Te- 

 trodon 3Iola we perceive, as it were, only scattered fibres 

 amid the membranes, and in Lophius piscalorius they are 

 nearly as soft. The other Tetrodons and Diodons, the 

 Balistes and the Ostracions, have denser bones ; and in 

 some species these parts can scarcely be distinguished 

 from those of the osseous fishes. It is certain also that 

 the bony frame-work of the fibro-cartilaginous kinds is 

 constructed on the same plan as that of the truly osseous 

 species, and not in accordance with those of the Chon- 

 dropterygii ; and it is in opposition to the known truth of 

 nature that both Artedi and Linna;us have denied them 

 the possession of opercula and branchiostegous rays. 

 The Balistes have even ribs, — their only osteological dif- 

 ference consisting in the granulation of their jaws ; while 

 the Sijngiuithi have regular bony jaws, although they 

 want the ribs and branchiostegous rays. 



The majority of osseous fishes have bones fully harder 

 than those of other animals, and it is quite a gratuitous 

 assumption to suppose that the observed longevity of cer- 

 tain species arises from the softer consistence of those 

 parts. Certain fish bones, in fact, exhibit neither pores 

 nor fibres, and appear almost vitreous to the eye. But 

 neither the osseous nor the cartilaginous kinds have ci- 

 ther epiphyses to the bones, or medullary canal within 

 them ; but there are some, such as the trouts, in which 

 the tissue of the bones is more or less penetrated by an 

 oilyjuice; while in others, such as the Dory, the inter- 

 nal portion continues cartilaginous, while the surface is 

 completely ossified. Finally, in certain species, while 

 the general skeleton is very hard, particular portions of 

 it are cartilaginous. Such are the bones which consti- 

 tute the head of the pike. 



When viewed in relation to their general structure, 

 the bones of fishes, like those of other vertebrated ani- 

 mals, are composed of an organic base penetrated by 

 earthy matter. The latter consists of phosphate of lime 

 and of magnesia, with oxide of iron, supposed to be unit- 

 ed to phosphoric acid. There is also a certain portion 



I It may be here noted, however, that certain malacopterygian kinds, such as carps and siluri, have the articulations of some of 

 the rays soldered together, in such a manner as to appear simply spinous. 



