lo8 



ICHTHYOLOGY. 



Introduc- consequently offers but a dull and feeble representative of 

 ''""■ that beautiful and most expressive organ, so full of life and 

 '('""^ animation in the higher tribes. 



The position, direction, and dimensions of the eyes of 

 fishes vary greatly. In some they have an upward aspect, 

 and are often very close upon each other ; in others they 

 are lateral, and so wide apart as to be even directed slight- 

 ly downwards. But of all anomalies, one of the most ex- 

 traordinary which their position presents, is that of the 

 Pleuronectes (such as tm'bot, flounders, soles, &c.). In 

 which the two eyes are placed, as it w ere, the one above 

 the other, and both u])on the same side of the head. In 

 certain species of the eels and Siltiri, they are so small as 

 to be scarcely visible ; while in other groiii)s, such as Pria- 

 ca7it/ius and Pomatonms, they siu'pass in proportional dia- 

 meter whatever is known of the same organs in the higher 

 classes. It may be said in general that the eye of fishes 

 is large, and that its pupil especially is broad and open ; a 

 character probably connected witli the necessity of collect- 

 ing whatever devious rays of light may penetrate the ob- 

 scure depth of waters. Fishes have no true eyelids. The 

 skin always passes over the eye, to which it is slightly ad- 

 herent ; and it is for the most part sufficiently transparent 

 for the passage of the solar rays. In some species, such as 

 eels, it passes over without the slightest fold or duplication ; 

 while in a few, for example, the Gcislrobranchus cacus of 

 Bloch, it continues quite opake, so as entirely to conceal 

 the eye. In others, as the well-known mackerel and her- 

 ring, it forms an adipose fold both before and behind ; but 

 these folds are fixed, and being unprovided with muscles, 

 have no mobility. Sharks have one, somewhat more move- 

 able, on the inferior margin of the orbit. The globe of the 

 eye itself is very slightly moveable, although, like that of 

 man, it is furnished «ith six muscles. Perhaps the most sin- 

 gular eye presented by the class of fishes is that of Anableps, 

 which has two cornea?, separated by an opake line, and two 

 pupils pierced in the same iris, so that one might deem it 

 double ; but there is only one retina, and a single vitreous 

 and crystalline humour. In accordance with the general 

 structure of the eyes of fishes (which we shall not further 

 detail), the nearly spherical form of the crystalline humour, 

 the immobility of the pupil, and the difficulty with which 

 it changes the length of its axis, we can scarcely doubt 

 that the vision of this class is comparatively imperfect. 

 Images must be but feebly painted in their retina, and 

 their visual perceptions must be indistinct and dull. At 

 the same time it is evident that they perceive their prey 

 from a considerable distance ; and the angler, who knows 

 either how rapidly they seize or how cautiously they avoid 

 his lure, and with what discrimination they sometimes pre- 

 fer one colour or kind of artificial fly to another, must be 

 impressed with the belief that the power of vision, at least 

 of certain species, is by no means devoid of clearness and 

 precision. 



The organ of hearing in fishes consists of little more than 

 the labyrinth, and that a much less complicated one than 

 the corresponding part in either qiiadrupeds or birds. 

 They have no external car, unless we may bestow that 

 name on a small cavity, sometimes slightly spiral, which 

 we find in the rays. It is however always covered by the 

 skin, and is not perceptible among the osseous fishes. A 

 i'ew of the latter, such as the genus Lepidolcprus, and certain 

 Mormyri, have merely openings in the cranium closed by 

 the skin, by means of which the vibrations of the element 

 by which they are surrounded may be conducted to the 

 labyrinth. In some other species, as Myripristis, the cra- 

 nium is open beneath, and its orifice is closed by a mera- 

 brano\is partition, to which the swimming bladder adheres ; 

 but these communications are very different from that 

 which takes place by means of the tympanum, and still 

 more by means of the Eustachian tube in other classes. 



Both these parts, as well as the bones, are in fact wanting Introduc- 

 in the class of fishes. Those who find in the bones of the tion. 

 operculum the four bones of the ear of man suddenly and 

 prodigiously developed, hazard such a notion merely on the 

 assumption that the bony pieces are the same in number 

 in all crania ; but it must be borne in mind, that neither 

 the form, nor the relations, nor the functions of these bones, 

 nor their nerves nor muscles, support such a comparison. 

 The ear of fishes, then, is much less complete than that of 

 quadrupeds, birds, or even of the majority of reptiles. 

 There is no doubt that they possess the sense of hearing ; 

 but it is merely a general sense of sound, and is in all 

 probability incompetent to perceive any variety or range 

 of intonation. In truth, the simple fact of fishes being as 

 a class entirely mute, is of itself a logical ground for be- 

 lieving that their perception of sound is extremely dull. 



A few lines may now be devoted to the consideration of 

 the sense of smell. The nostrils of fishes are not so placed 

 as to be traversed either by air or water, in connection 

 with the act of respiration. They consist merely of two 

 openings, situate near the extremity of the muzzle, and 

 lined by the pituitary membrane, which is raised in ex- 

 tremely regular folds. In the ordinary fishes, the bones 

 which Cuvier regards as the nasal serve as the arch or 

 covering ; while the vomer, the maxillary, and inter-maxil- 

 lary contribute to sustain the sides, the first sub-orbitary 

 forming the inferior portion. The shape of the nostrils is 

 sometimes oblong, sometimes round or oval. They are 

 placed either at the end of the muzzle or on its sides ; 

 sometimes on its superior face, and even occasionally, as 

 in skates and sharks, on its under surface near the angle of 

 the mouth. In the lamprey they are approximate on the 

 top of the head, and open by one common orifice. In the 

 great majority of fishes, perhaps in all the osseous kinds, 

 each nostril opens by two orifices, the one posterior to the 

 other, and in some cases at a considerable distance. These 

 are what are called double nostrils ; an inaccurate term, in 

 as far as each pair of holes leads only to a single cavity. 

 The margins oi' the anterior orifice are often tubular, as 

 in the eel, and sometimes a single side of the tubular mar- 

 gin is prolonged into a tentacular appendage, as in several 

 JSiluri. In the genus Lophius the nostrils are borne upon 

 a little pedicle, so as somewhat to resemble mushrooms. 

 Various other modifications are observable in different ge- 

 nera, although not necessary to be here narrated. It does 

 not appear, at least in the osseous fishes, that the envelope 

 of the nostrils possesses mobility, or that the orifices are 

 furnished with muscles by means of which they can be 

 opened and shut. 



It is certain, however, that fishes possess the faculty of 

 perceiving odours ; that various scents attract or repel 

 them ; and there is no reason to doubt that the seat of that 

 perception lies in the nostrils. It may be reasonably con- 

 jectured that its strength depends mainly on the degree of 

 development produced by the number and extent of the 

 interior folds. 



In regard to the sense of taste in fishes, it is evident that 

 as, with few exceptions, they swallow their food rapidly 

 and without mastication, their perception of that faculty 

 nmst be in noways acute. The same may be inferred 

 from the fact of their tongue being almost immoveable, 

 often entirely osseous, or beset with teeth or dental plates, 

 and from its receiving very slender nerves, and these but 

 i'evi in number. Even those species of which the jaws 

 are so armed as to enable them to cut and bruize their ali- 

 ments, cannot long retain the latter in their mouths, on 

 account of the position and the play of the respiratory or- 

 gans. No salivary glands discharge their moisture on the 

 organs of taste. The tongue itself is not seldom entirely 

 wanting; and even when it exists in its most distinct and 

 apparently fleshy state, it consists merely of a ligament- 



