ICHTHYOLOGY. 



163 



Introduc. common alike to the Mollnsca and to fislios, can they be 

 tion. brought into relation with those connections which the 



'""'y^^ latter exhibit with the other vertebrated classes? By 

 what passage does nature conduct us from the one to the 

 other ? It is certainly by no means difficult, while dis- 

 regarding numerous disagreements, so to compose a defi- 

 nition as to embrace only those points which they possess 

 in common ; but that definition assuredly will always re- 

 pose upon a pure abstraction of the mind, a definition 

 simply nominal, an assemblage of vain words, which can 

 never be represented by a harmonious and existing plan, 

 notwithstanding whatever extraneous details may be col- 

 lected or conceived in support of such visionary views. 

 By a like procedure, there is in truth no two things, how- 

 ever remote or dissimilar, which may not be so allied ; for, 

 whatever their disresemblance, there will always be some 

 particular point or other in which they may be found to 

 agree. But when we look to the characters in which ob- 

 jects differ, we shall find reason to view the subject in an- 

 other light. The heart itself in those MoUusca which have 

 only one, is placed in a contrary mode from that of fishes ; 

 it is at the junction of the branchial veins and arteries of 

 the body that that organ is attached ; in several the mem- 

 bers are placed upon the head, in others the generative 

 system is lateral, and frequently the respiratory organs 

 are placed above those of digestion, and extend more or 

 less over the dorsal surface. Perhaps all that can be said 

 regarding any positive or important relationship between 

 MoUusca and fishes is, that both classes are possessed of 

 branchiae. 



It may indeed be observed, that whenever we proceed 

 from these purely verbal or metaphysical formula, we find 

 ourselves lost among the most inadmissible comparisons. 

 According to one theorist, the shells of bivalves represent 

 the opercula of fishes ; according to another, the buckler 

 of the cuttle-fish is a true fibrous bone ; according to a 

 third, the large scales of the sturgeon, and the spines of 

 the diodons, are to b^ regarded as an external skeleton. 

 Others search for the desired analogies among the Crus- 

 tacea, of which the margins of the thorax represent the 

 opercula. Beneath these margins the branchiae actually 

 occur, but if we continue the comparison, all is changed. 

 The medullary cord is towards the abdomen, the heart 

 towards the back, and the latter organ, as among the 

 MoUusca, receives the blood from the branchiae, but does 

 not send it thither. Finally, some observers, apparently 

 despairing of their transcendental cause, perceive the rays 

 or spiny apophyses of vertebrated animals in the legs of 

 the Crustacea, forgetting that, were it so, an obvious de- 

 gradation rather than amelioration of organic structure 

 must have befallen the class of fishes. 



The affinity of fishes toother classes of vertebrated ani- 

 mals is much better founded. At least we here find the 

 commencement of sensible relations in the number of or- 

 ganic systems, and in their mutual connections ; but we 

 are still far from discovering a progressive and continuous 

 course. We cannot in this place report the conclusive 

 reasoning of Baron Cuvier regarding the distinctions of 

 these classes. We shall merely state his conclusion to be, 

 that if there is a resemblance between the organs of fishes 

 and those of the other great groups of the animal king- 

 dom, it is only in so far as the functions of such organs 

 are similar ; that if we assert either that fishes are Mol- 

 lusca of an ameliorated or higher grade, or that they re- 

 present a commencing or fcetal state of reptiles, we can do 

 so only in an abstract or metaphysical acceptation, and 

 that even with that restriction we by no means convey an 

 accurate notion of their organic structure ; that we can- 

 not regard them either as links of an imaginary chain of 

 successive forms (of which none could serve as the germ 

 of another, since none is capable of a solitary or isolated 



existence), nor of that other chain, not less fanciful, of si- Introduc- 

 multaneous and transitionary forms, which has no reality ,^l°|]l^ 

 but in the imagination of certain naturalists, more poeti- ~^i~^-^ 

 cal than observant. They pertain in truth, and solely, to 

 the actual chain of co-existent beings, — of beings neces- 

 sary to each other, and which by their mutual action 

 maintain the resplendent order and harmony of created 

 things. 



These are thy (rlorious works, F.irent of good. 



Almighty ! Thine this universal frame. 



Thus wondrous fair ; Thyself how wondrous theri I 



Unspeakable, who sitt'st above these heavens. 



To us invisible, or dimly seen 



In these thy lowest works; yet these declare 



Thy goodness beyond thought, and power divine. 



SECT. Xr. THE CLASSIFICATION OF FISHES. 



The class of fishes is of all others the most difficult to 

 divide into orders, according to fixed and perceptible 

 characters. We shall here give a brief view of I3aron 

 Cuvier's arrangement, the details of which we shall after- 

 wards exhibit in our systematic view. 



Fishes are divisible, in the first place, into two great and 

 distinct series, viz. Fishes pkoperly so called, embra- 

 cing the great majority of species ; and Chondboptery- 

 GiAN or Cartilaginous Fishes, such as sharks and 

 rays. 



The general character of the latter series consists in 

 the absence of the bones of the upper jaw, the place of 

 which is supplied by those of the palate. Their entire 

 structure also exhibits sundry analogies, to be afterwards 

 described. Cartilaginous fishes are further divisible into 

 three principal orders. 



1st. Cyclostomi, the jaws of which are soldered into 

 an immoveable ring, and the branchiae open by means of 

 numerous holes. Example, the Lamprey. 



2d. Selaciiii, which possess thebranchix of the Cyclos- 

 tomi, but not their jaws. Example, Sharks. 



3d. Sturiones, of which the branchial opening is in 

 the usual fissure-like form, and furnished with an opercle. 

 Example, Sturgeons. 



The other great series, or that of the Ordinary Fishes, 

 presents a first subdivision into those in which the maxil- 

 lary bone and the palatine arch are fixed to the cranium. 

 They constitute Cuvier's order Plectognathi, which 

 comprises two families, the Gy.mnodontes and Sclero- 

 DERMi. Examples, the genera Diodo7i and Ostracion. 



The next subdivision of the ordinary fishes contains 

 certain species with perfect jaws, but the branchiee of 

 which, instead of being comb-shaped, resemble a series of 

 small tufts. They constitute an order called Lopho- 

 branchii, which comprises the two genera Syngnathus 

 and Pegasus of Linn. Example, the Pipe-fish. 



Of the ordinary fishes there then remains an immense 

 assemblage, to the general classification of which no other 

 characters can be applied than those of the external or- 

 gans of motion. After a long and laborious research. 

 Baron Cuvier became satisfied that the least objection- 

 able of these characters is still that long ago employed 

 by Ray and Artedi, drawn from the nature of the first 

 rays of the dorsal and anal fins. Thus the great body of 

 the ordinary fishes is divided into Malacopterygii, in 

 which all the rays are soft, with the occasional exception 

 of the first of the dorsal, or of the pectorals ; and Acan- 

 thopterygii, in which the first portion of the dorsal, or 

 the first dorsal if there are two fins of that kind, is al- 

 ways supported by spinous rays, and where some similar 

 spines are also found in the anal fin, and at least one in 

 each of the ventrals. 



Of these two last-mentioned groups, the former, or 



