FISH 



489 



In the case of sight, the state of things is very dif- 

 ferent, and fishes may, especially from the microscopic 

 form of the crystalline lenses of their eyes, have as per- 

 fect vision at depths to which we suppose only a small 

 portion of the light of the sun ever reaches, as we have 

 in the noontide beams of the luminary. We must not 

 judge of the capacity of any eye for seeing under 

 water, from the difficulty that one has of seeing into 

 it ; because, without any reference to the clear or 

 muddy state of the water itself, the quantity of light 

 which the surface reflects when the rays fall obliquely 

 upon it, is greater than that which is not out of the 

 water. Of this we have a case nearly parallel, when 

 we stand in a very oblique position with regard to a 

 window, and endeavour to see what is going on inside. 

 The glass of the window may be nearly as transpa- 

 rent as the air itself, and it may be perfectly flat, so 

 as not to break the reflected light ; but the more 

 transparent, and the more flat and smooth, the more 

 completely does it obstruct our vision by the reflected 

 light, if our position has the requisite degree of 

 obliquity. But notwithstanding our inability to see 

 through the window into the apartment under these 

 circumstances, the people in the apartment may be 

 enjoying even a quantity of light which is painful to 

 them, and they may be capable of discovering the 

 most minute object, not only inside the room but 

 through the window. 



The situation of fishes in the sea is much the same 

 as that of the inmates of the room in this illustration, 

 and we, the observers of the fishes, are like the spec- 

 tators out of doors, incapable of seeing what goes on, 

 either if our position is oblique, or if the light falls 

 obliquely on the surface. And we have the evidence 

 of direct observation in proof of this. There is no 

 reason why the water of the sea should be more 

 transparent in the regions of the equator than in 

 those of the poles ; and yet, from the mere fact of 

 the solar light falling nearly perpendicular upon the 

 surface of the water in those seas, they are as clear 

 as crystal, and one can see the whole of the opera- 

 tions that are going on even though the depth be 

 forty fathoms or more. In our latitudes we can see 

 but a very small depth into the sea, and therefore 

 the operations which go on under the surface are a 

 sealed book to us. But it is only we who are thus 

 left in the dark, for there is abundant light for every 

 eye which is under the water. Those who have so 

 practised diving that they can do it with the eyes 

 open, are able to see the smallest object at the 

 greatest depths which they can reach ; and there is 

 no doubt that, from the peculiar structure of the eye 

 in fishes, and the increase of the field of view in pro- 

 portion to the depth, they can see the most minute 

 objects at the greatest depths which they inhabit, and 

 that, at al! depths, sight is the sense on which they 

 chiefly depend. Still fishes have organs both of 

 smell and of hearing, and without a slight notice of 

 these our sketch of them would be incomplete. 



The organs of smell vary more than in the mam- 

 malia or birds. In many, the nostrils have only the 

 opening on each side ; but in others, this is parted 

 by a septum which gives them the appearance of hav- 

 ing four nostrils. Sometimes the openings are round, 

 sometimes oval, and sometimes they are longitudinal 

 slits. They are either on the mouth or between the 

 eyes, or in an intermediate position ; and they have 

 occasionally the form of short projecting tubes. They 

 are furnished with a few muscular fibres, and so must 



be capable of some motion ; but to what extent, and 

 for what purpose, it is by no means easy to deter- 

 mine. 



On examining the inside of the nostril, we find in 

 sharks and rays a large lamina, which extends the 

 whole length of the opening, with smaller parallel 

 laminae branching off from it on each side like the 

 teeth of a crab ; while in most fishes of both divisions 

 these laminae are like rays with a tubercle in the 

 centre. In the membrane which lines the nostrils of 

 the pike, the vessels are black ; but in most fishes 

 they are red ; and there are between the nasal vessels 

 in all fishes, papilla? which discharge a thick mucus. 

 The olfactory nerves, at their origin, form swellings or 

 knots, so large as frequently to have been mistaken for 

 the real brain. These tubercles in skates and sharks 

 are united into one homogeneous medullary mass, from 

 each of the lateral parts of which the olfactory nerves 

 arise. In the flounder, the herring, pike, perch, and 

 salmon, there are two pair of tubercles, the anterior 

 of which is smaller than the other. In the cartilagi- 

 nous fishes, as the skates and shark, the olfactory 

 nerve is very soft. It is, in them, a bulb which passes 

 obliquely forward towards the nares, which are at a 

 greater or less distance from the brain, according to 

 the species. The spinous fishes have the olfactory 

 nerve very long and slender. In those which have 

 the snout elongated, this nerve is received^nto a car- 

 tilaginous tube. In those with short snouts, the 

 nerve is surrounded by a fine membrane only, which 

 appears to be the same as that which contains the fat 

 or oily humour that covers the brain. In the haddock, 

 and some other fishes, the olfactory nerve, in its course 

 from the brain to the nose, passes through a cineritious 

 ball, which resembles the cineritious matter connected 

 in our body to the olfactory nerve within the cranium. 

 When the olfactory nerve arrives behind the folded 

 membrane which we have described, it is dilated to 

 be applied to the whole of its internal and convex 

 surface. In some fishes no previous enlargement 

 takes place ; while in others the nerve swells into a 

 real ganglion. When expanded, it has been compared 

 to the retina, but the filaments of which it is composed 

 are more distinct. 



As a specimen of the opinions which are held by 

 those who speak and write with not the most profound 

 reflection, but which sort of opinions are unfortunately 

 the most prevalent both in conversation and in books, 

 we shall quote a short passage from Dr. Shaw's General 

 Zoology, which, however, the reader, who bears in 

 mind the readiness with which artificial flies and 

 wooden minnows are taken, will perceive, carries its 

 own refutation. " If," says Dr. Shaw, " you throw a 

 fresh worm into the water, a fish shall distinguish it 

 at a considerable distance ; and that this is not done 

 by the eye is plain from observing, that after the same 

 worm has been a considerable time in the water, and 

 lost its smell, no fishes will come near it ; but if you 

 take out the bait, and make several incisions into it, 

 so as to let out more of the odoriferous effluvia, it 

 shall have the same effect as formerly. Now it is 

 certain, that, had the animals discovered this bait with 

 their eyes, they would have come equally to it in 

 both cases. In consequence of this smell being the 

 principal means they have of discovering their food, 

 we may frequently observe them allowing themselves 

 to be carried down with the stream, that they may 

 ascend again leisurely against the current of water ; 

 thus the odoriferous particles swimming in. that 



