ICHTHYOLOGY. 



153 



Iiitroduc- fishes, from which in fact they essentially differed in no- 

 t'O"- thing. But he satisfied himself that the singular genus 



■"^-Y"*^ Syngnathus, of which tiie form and economy are so re- 

 markable, were distinctively characterised by their bran- 

 chiae, in the form of tufts (hence the title of lophobraiichial 

 fishes), concealed beneath an opercle which permits the 

 water to escape only by a small opening towards the nape 

 of the neck ; and that the genera Diodon, Tetrodon, Os- 

 tracion, and Balistes, independently of the singularity of 

 their general form, and the incompleteness of their skele- 

 ton, have the jaws, and in general all the bones of the head, 

 somewhat differently arranged from the corresponding parts 

 in tlie generality of fishes, the upper jaw and the palatine 

 bones being articulated with each other, and with the vo- 

 mer, by immoveable sutures — a structure which leaves 

 them much less freedom in the opening of their mouths, 

 and is also the cause (in connection with the tightness of 

 the tegumentary envelope which fastens down the bran- 

 chial apparatus) of so many naturalists having failed to per- 

 ceive that the genera in question were furnished with rays 

 and opercula like other species. 



But these groups once separated, there remained nine 

 tenths of the whole class of fishes, among which the first 

 great distinctive division which presents itself is, into such 

 as have soft fins, or of which tlie rays are branched and 

 articulated, and into such as have spiny fins, of which a 

 portion of the rays consist of pointed bones without 

 branches or articulation, — two primary divisions, corre- 

 sponding to the great groups named respectively Mala- 

 coPTERVGii and Acanthopterygii by Artedi. Even 

 this principle of classification is not universally prevalent; 

 for, in its practical application, we are obliged to keep out 

 of view the first rays of the dorsal and pectoral fins in cer- 

 tain species of the genera Cyprimis and Silurus, in which 

 these rays exhibit strong and solid spines, although we still 

 class them with the Malacopterygii, or soft-finned division.' 

 In like manner, there are, among the other great division, 

 corresponding exceptions to the acanthopterygian character, 

 as in the blennies and certain Labridae, of which the spines 

 are so small, so feeble, or so few in number, as almost to 

 escape detection. However, if the principle referred to is 

 not quite precise in relation to these slight anomalies, it is 

 on the whole well founded, and certainly does not force us 

 to separate numerous species which nature has approxi- 

 mated. 



The same cannot be asserted of those distinctions which 

 naturalists have sought to establish on other principles, nor 

 of those on which so many of the secondary divisions have 

 been founded. Thus the general form of the body, and 

 tlie absence of the ventral fins, the characters assumed by 

 Ray, anterior to those deduced from the spines, force a 

 heterogeneous grouping of the eels, the gobies, the Syng- 

 nathi, the Xiphias, and the moon-fish. Linnaeus was the 

 first (in the tenth edition of the Systema Natura), while 

 neglecting the distinction of the spiny rays, to imagine the 

 division of ordinary fishes into apodal, jugular, thoracic, 

 and abdominal, according to the absence or position of the 

 ventral fins ; and in so doing obliged himself to place the 

 genera Xiphias, Trichiurus, and Stromateus with the eels 

 and Gytmwti, the Gadi between the weevers and the blen- 

 nies, Pleuronectes between Zeus and Chatodon, and the Aru- 

 pAaca7j</«' as intermediate with Silurus and Loricaria. Va- 



rious modifications have since been proposed of the Lin- Introduc- 

 noean arrangement, but our present limits will not admit of tion. 

 our entering upon these as exhibited in the various works "^"V*^ 

 of Gouan, Lacepede, Dumeril, Risso, Rafincsque, Goldfuss, 

 Oken, and others who have laboured to amend the modern 

 system.^ 



SECT. II. THE EXTERNAL FORM AND CHARACTER 01" 



FISHES.^ 



The form and structure of fishes are as admirably adapt- 

 ed for rapid movement through the water, as are those of 

 birds for that aerial motion called flight. Suspended in a 

 liquid element of almost equal specific gravity with them- 

 selves, external organs resembling those of birds in size 

 would have been disproportioned and unnecessary ; but the 

 air-bladder (the functions of which, by no means entirely 

 understood, have never been satisfactorily explained in all 

 their bearings) is known to possess the power of contrac- 

 tion and dilatation, the exercise of which is followed by 

 a corresponding descent or ascent of the animal's body. 

 Thus a small, central, and inconspicuous organ eiiects, in 

 the easiest and most simple manner, the same object which 

 even the soaring eagle or giant condor can only attain by 

 great exertion of the wings, and after laborious and fre- 

 quently repeated gyrations. We shall ere long, however, 

 have occasion to observe, that the air-bladder, although es- 

 sential to the economy of such species as possess it, is by 

 no means indispensable to the class of fishes, as in many 

 tribes it is entirely wanting. 



Fishes being without a neck, and the part called the tail 

 for the most part equalling at its origin the portion of the 

 trunk from which it springs, the prevailing shape is some- 

 what uniform, diminishing gradually towards either end. 

 Doubtless, however, a vast variety of form is exhibited in 

 a class which is now calculated to contain from six to eight 

 thousand collected species. Of these forms a sufficiently 

 accurate idea may be acquired by inspecting the numerous 

 plates which accompany the present treatise, and we shall 

 therefore not attempt any further verbal illustration of the 

 subject, although we shall add a few notices regarding the 

 general aspect and character of the principal external parts. 



The mouth of fishes either opens from beneath, as in the 

 rays, or at the extremity of the muzzle, as in the majority 

 of the class, or from the upper surface, as in Uranoscopus. 

 It also varies greatly in its relative dimensions, from the mi- 

 nute perforation of Centrisctis, to the vast expansion of the 

 angler fish. 



Exteriorly only two of the organs of the senses are visi- 

 ble, the orifices of the nostrils and the eyes. The former 

 may be simple, as in the rays and sharks, or double, as in 

 the generality of osseous fishes ; and they differ in their 

 position in relation to the jaws, the eyes, or the extremity 

 of the muzzle. The eyes vary extremely in respect to 

 size in the different species, and even sometimes disappear 

 entirely beneath the skin ; and they also differ greatly in 

 their position, being usually placed laterally, one on each 

 side of the head, although in Uranoscopus (as the name 

 implies) they look upwards, and in most of the flat fishes 

 they both occupy the same side. 



In regard to those important organs, the branchiae or 

 gills, a single family alone, the chondropterygian fishes. 



' These epines, however, as Cuvier remarks, are formed, in the two genera above named, by the agglutination of a multitude of 

 smaller parts, of which the articulations, though not obvious, are perceptible. 



* For critical notices of their works, see the 1st volume of the Hitt. Nat. des Poissons. 



' We may here premise, that in the ensuing sections several interesting and important particulars in the structure and physiology 

 of fishes are very slightly, or even not at all, touched upon, in consequence of their having been already detailed in the article 

 Comparative Anatomy of this work. (See vol. iii. p. 1, &c.) We deemed it more advisable that the reader should be made to 

 incur the slight inconvenience of referring occasionally to a separate treatise, than that the present publication should be burdened 

 by a repetition of the same subject. U 



VOL. XI 1. 



