FISH. 



487 



to injuries. We may therefore consider it as a general 

 Jaw that where fishes inhabit the water, and do not bury 

 themselves at least over the eyes in the ooze at the 

 bottom, the size of the eye is in proportion to the 

 depth. Thirty or forty fathoms may perhaps be con- 

 sidered as the average depth of a cod fish on the 

 ground banks ; and the eye of a fish of this descrip- 

 tion is at least as large as that of an ox. Thus the 

 size of the eye guides us to the position which the 

 fish holds in the water ; and in like manner the situa- 

 tion of the eyes points out in what direction the fish 

 looks out for its food. Those which lie at the bottom, 

 or swim near the bottom, and look for prey over 

 them, have the eyes in the upper part of the head, 

 and often very near to each other ; and in order to 

 answer this habit, the mouth of such fishes very gene- 

 rally opens upwards also, that is to say, the lower 

 jaw projects beyond the upper one, and rises up in 

 front of it. On the other hand, if the fish has to seek 

 its food below it, the eyes are placed wide apart, and 

 fishes of this kind very frequently have the muzzle or 

 frontal line from the eyes sloping downwards as if 

 truncated, and the opening of the mouth below. 

 Fishes which follow their prey in level chase, have 

 the eyes placed more nearly in the situation of those 

 of land animals of the chase ; and in them, what- 

 ever may be the nature of the prey, the opening of the 

 mouth is pretty nearly straight. 



This connection between the form and position of 

 the eyes, and the mouth of fishes, and also with the 

 depths at which they feed, and the direction in which 

 their food is situated with regard to them, is very 

 important in the natural history of fishes, and affords 

 perhaps a surer guide to the character of any " strange 

 fish " that we meet with, than half the characters 

 which are given, or which can be given in the systems. 

 Indeed, systematic ichthyology is very imperfect in 

 this respect ; for even where the characters of the 

 genus, the species, or even the larger division, are 

 given with the greatest accuracy, they do not of them- 

 selves give the slightest indication of the part of the 

 sea in which we are to seek for that species of fish 

 with the greatest certainty of success ; and it would 

 certainly be desirable to combine something of this 

 kind with the systematic view, though to carry it into 

 details would most likely be a work of immense labour 

 and much uncertainty. It would also be a good plan, 

 if the execution of it were possible, to connect the 

 qualities of the fish as food, with the characters indi- 

 cating the depths at which they are found j but this 

 is a point to which we shall have occasion to recur. 



The eyes of fishes are placed \\\fossce or sockets in 

 the bones of the head, much in the same way as those 

 of the other vertebrated animals ; but they are in 

 general destitute of eye-lids, neither have they any 

 projecting arch in the form of an eyebrow, or any of 

 that apparatus which in the land vertebrata is employed 

 in lubricating and cleaning the eyes. Whether fishes 

 know sorrow we cannot tell ; but we are sure that 

 they cannot " weep over their woes," for they have 

 no tears. In the moon fish ( Tctrodon mola) however, 

 the eye is in great part covered by a circular lid, which 

 has merely a perforation in the middle for admitting 

 the light. In the greater number the skin passes 

 over the eye without any division, so that that organ 

 is as well defended as any other part of the bod}-, 

 only the skin over it is transparent. In removing the 

 skin from a common eel, there is no perforation an- 

 swering to the eyes. The whole skin appears of 



equal strength, only there are two little patches cor- 

 responding to the eyes, which are transparent and 

 colourless. 



But in some fishes there is not this transparent 

 spot, or window for the accommodation of the eye. 

 In some the texture, and even the colour, of the rest 

 of the skin extends to the part which covers this 

 organ. In the trunk fishes (Ostmcions) there are the 

 same striae or rugosities in the skin over the eyes, as 

 in that of the surrounding parts ; and in that singular 

 inhabitant of the northern seas (Gastrobranchus cascus, 

 Myjcinc ghdinosa of Linnseus,) the common integu- 

 ments which pass over the eyes are so exactly of the 

 same colour and texture as the rest, that the animal 

 appears to have no eyes at all until the skin is 

 removed. 



The element in which fishes live, by the constant 

 motion of the water, renders the use of eyelids and 

 lubricating fluids perfectly unnecessary ; and their 

 exposure to the same fluid under a heavy pressure, 

 owing to the great depth, requires a far more firm 

 covering than the common coat which encloses the 

 aqueous humour of an eye which is used only in 

 the air. A projecting eye, or one convex outwards, 

 would be equally inconvenient, and thus the surface 

 of the eyes in fishes is flat ; but this is compensated 

 by the greater magnifying power of the crystalline 

 lens. The flat cornea of the eye in fishes, besides 

 being that which sustains least injury from the pas- 

 sage of the fish through the water, and from the 

 chance of striking against obstacles, has some advan- 

 tages in the greater quantity of light which it sends 

 to the sentient part of the eyes, than would be sent 

 by a convex surface. It is only at the middle of 

 such a surface that the whole of the light falling upon 

 it enters ; for everywhere else a portion is reflected 

 off, corresponding to the angle at which the circular 

 surface turns away from a plane at right angles to 

 the axis of its centre ; and by this means, great part 

 of the light which falls upon the external surface of a 

 very round or protuberant eye, is dispersed through 

 the surrounding atmosphere, and would be lost for all 

 useful purposes in vision. But when the surface of 

 the eye is flat, as it is in fishes, there is no more light 

 reflected away from one part of it than from another ; 

 and therefore, of such quantity of light as may reach 

 the eyes of fishes in the depths of the sea, there is 

 much less lost than there is of that which falls upon 

 the convex eyes of land animals. No doubt there is 

 a much more scanty supply of light under the water, 

 especially at considerable depths, than there is upon 

 the land ; but it is this which, more than any thing 

 else, shows the beautiful adaptation of the eye to the 

 circumstances under which it is used ; and no one 

 who reflects on the subject will fail to perceive that in 

 the coincidence of this with all the other advantages 

 which the fish derives from the peculiar structure of 

 this organ, there is evidence of wisdom far surpassing 

 not only the wisdom of man, but the estimation of the 

 human mind, in any other feeling than that of simple 

 adoration. 



In fishes the general form of the entire eye with its 

 coats, its lenses, and its humours is nearly that of a 

 hemisphere, of which the flat side is external, and the 

 interior one spherical. In the skate, the superior 

 part is also flattened, so that the vertical diameter is 

 to the transverse as one to two. This flatness of 

 the anterior part of the eye is compensated by the 

 spherical form of the crystalline lens. This body is 



