486 



FISH. 



centres all the ducts are shut, and in their course 

 they have no communication with each other. In 

 these two central parts, or on the beginning of the 

 mucous ducts, a pair of nerves nearly as large as the 

 optic, terminates, and which is a curious circumstance 

 with respect to them, they are white and opaque in 

 their course, between the brain and their ducts, but 

 when they divide, they become suddenly so pellucid 

 that it is impossible to trace them further, or to dis- 

 tinguish them from the coats of the ducts." 



In the bony fishes, the distribution of this mucous 

 secretion is somewhat different. The orifices from 

 which it is discharged are principally either on the 

 forehead, or along the lateral line. This line by the 

 way is a peculiar marking in fish. In some it is not 

 found, as in the lamprey ; in most fishes it is single ; 

 but in some, as in the launce (ammodytes), it is 

 double ; and there are some fishes, indeed the greater 

 number, which have it straight ; but in others it 

 makes a singular bend upward, opposite to the cavity 

 of the body. This line is differently coloured from 

 every other part of the side of the fish ; and its 

 colour fades sooner after death than the colour of 

 any other part. This, together with the accumula- 

 tion of the mucous ducts upon it, shows that it must 

 have some important connection with the living 

 action of the fish ; though what this connection is 

 has not been ascertained. The mucus itself has not 

 been analysed with sufficient care, but it seems to be 

 something in the nature of albumen, probably in 

 nearly the same state as it exists in the epidermis, 

 though it is liquid in the one case, and solid in the 

 other. It is indeed a substance which, though plen- 

 tiful, is not very easily examined, at least in such a 

 manner as to judge of it while the fish is living and 

 under the water, because it seems so intimately 

 connected with the nervous system of the fish, that 

 there is no knowing how great a change may be 

 produced in it by death, or even by exposure to 

 the atmosphere. 



Organs of sensation. The senses of fishes, like 

 those of all other animals, form a very important part 

 of their history ; and we know from various facts, that 

 in many fishes, not only particular senses, but sensa- 

 tion generally must be very acute, from the readiness 

 with which they are affected by slight changes of the 

 weather. In a trouting stream for instance, when 

 the sun is under a cloud, and that cloud brings, as it 

 very often does, a slight curl upon the water, the 

 trout will rise to the fly with the greatest readiness ; 

 and also be seen sporting about in all directions 

 near the surface ; but as soon as the cloud passes, 

 and the ripple along with it, not a trout will rise to 

 the most skilful angler ; and one may observe them 

 lying perfectly still near the bottom of the shallows. 

 Under those circumstances there can be little difference 

 of temperature in the water, for the two may succeed 

 each other several times in the course of a few hours, 

 and therefore the trout must be in some way sensi- 

 ble to the influence of light. The same species of 

 fish, and many others, are also remarkable for the 

 acuteness of their vision. Every angler in clear 

 streams knows how vain it is to tempt a trout, if 

 either his shadow or his reflection is thrown upon the 

 water ; and even if the angler is on the right side, 

 the passage of a countryman along the opposite bank, 

 or a cow coming to drink, may spoil his sport for the 

 day. Of the hearing of fishes we know less ; but we 

 do know that water is a conductor of sound in a pecu- 



liar way, though, aswecannot make our experiments on 

 a direct parallel, our own ears being of a different struc- 

 ture from those of fishes, we can arrive at no very 

 conclusive result on the subject. As to the sense of 

 smelling, though some have gone so far as to say 

 that a trout knows a living worm from a dead one by 

 the smell, yet as the same sense does not enable the 

 very same trout to distinguish an artificial fly with a 

 hook in it, from a real fly upon the water, we must 

 conclude that this sense is exceedingly imperfect. 

 Of taste fishes can have but little, and indeed no 

 animals but such as masticate their food, or at all 

 events have soft tongues, have this sense in any high 

 degree. But fishes, at least with very few excep- 

 tions, swallow indiscriminately almost any substance 

 which is floating ; and sailors sometimes amuse them- 

 selves with "giving a shark his grog," as they term 

 it, that is throwing a corked empty bottle overboard, 

 in order that a shark may swallow it. 



The brain in fishes, if we are to suppose that the 

 acuteness of sensation bears any proportion to the 

 development of that organ, is very small and very 

 soft. In the tunny it is less than one seventeen 

 thousandth part of the body ; and in carp, which have 

 it in a greater proportion than most of the species that 

 have been examined, it is less than the five-hundredth 

 part. The peculiar manner in which the brain of the 

 whole finny race is developed, or rather the portions 

 of it which have the greatest development, would 

 lead us to conclude that, if we are to connect the 

 faculties and propensities of the animal with this 

 organ, the chief propensities of fishes are those that 

 relate to mere feeding and motion. 



Of the peculiar organs of sense, the eye is the most 

 conspicuous, and in all probability the most useful 

 to the animal. -As is the case with all vertebrated 

 animals, fishes have only two eyes, placed, generally 

 speaking, in opposite sides of the mesial plane. The 

 flat fish no doubt form an apparent exception to this ; 

 for in the usual way of regarding the darker coloured 

 side as the back, and the lighter coloured one as the 

 belly, the eyes are always on the upper or back part, 

 and towards one side of the mouth, sometimes the 

 left side, and in other species the right, as will be 

 mentioned in the article FLAT-FISH. But this apparent 

 deviation from the typical, and indeed the invariable 

 position of the eyes in vertebrated animals, is not real 

 in the fishes under notice. There is a twist in the 

 neck, or at all events in the upper portion of the 

 spinal column, which turns the mesial plane in an ob- 

 lique direction ; so that when it passes from fin to 

 fin in the body of a flounder, it passes through the 

 head in a curve, from a point between the eyes 

 through the mouth to the middle of the lower jaw. 

 In their size the eyes of fishes vary considerably ; 

 and though the general law be that the eye is large in 

 proportion as the fish inhabits the deeper water, yet 

 there are some exceptions. Thus in some species of 

 eel the eyes are so very minute, that they are barely 

 visible, even in a tolerably large specimen. But the 

 exception here is also more apparent than real ; for 

 though those eels do inhabit the bottom of those waters 

 in which they are found, yet they are never found at 

 any great depth. Besides, eels live partly in the water, 

 and partly in the mud, being as it were a sort of 

 water moles ; and therefore like the moles which bur- 

 row in the ground, and almost all animals which enter 

 partly or wholly into the soil, they have less need of 

 large eyes, and such eyes would be much more liable 



