But so far we have only examined the one-half of this question. It is perfectly known to fishermen that many species, which, in summer, frequent the shallow seas, ap parently for the purpose of spawning chiefly, retire to the great depths in winter ; and, as these persons suppose, to to avoid the cold. The regions of darkness seem to be their proper residence ; while, like the salmon and other migratory fishes, they are merely visitors in those of light. But, besides this, a very large proportion of all the fishes of the sea only preys by night, while there are some that do so by day, and others are ready for their food at all times. In the polar regions, and in the depths of winter, there can for a long period be no light in the sea, what ever faint glimmering the atmosphere, the planets, or the aurora, may yield for the inhabitants of the land. Yet here many fishes, and most conspicuously, some of the whales and the sword-fish have their perpetual residence. These animals can have no light for a long time, particularly in their deep waters, unless they find it in their own bodies, or in that of their prey. The food of the great whale, consisting of various insects and worms, very commonly shrimps, such as the Cancer oculatus, resides at the bot tom as well as on the top of the sea ; and there cannot, therefore, be any doubt that, even in summer, but most assuredly in winter, it feeds in regions that are inacces sible to light.
Our readers may now see the conclusions which we are inclined to draw respecting the final cause or purpose of this property of phosphorescence in fishes. It. is ne cessary to their general intercourse, and indispensably so in those particular cases just mentioned. Without it, in the deeper seas they would be unahle to discover their prey at any time ; nor, in our shallower ones, could they do so at night. Whatever diminution of light is felt by us during that period must, in a far greater degree, be experienced in the sea, even at small depths. Without such a provision, all intercourse between fishes must, cease in the night ; whereas we know that it is then of ten most active. We do not, however, mean to say, that the light of fishes supplies the place of the sun, or that it is intended to produce a general illumination of these ob scure regions. The main purpose of it seems to be, to indicate the presence of the object which forms the prey, to point out where the pursuit is to be directed. For that reason it seems to be particularly brilliant and decided in those inferior animals,which, from their astonishing powers of reproduction, and from a state of feeling apparently lit tle superior to that of vegetables, appear to have been in a great measure created for the supply and food of the more perfect kinds. Thus also it is diffused through every,
even the minutest animalcula, as all these seem in their turns to be destined to the same end, among others, mu tual enjoyment and mutual destruction.
It is also not improbable that the light which fishes pos sess enables them to discover their own food, or to guide themselves, as well as to betray themselves to their ene mies. We might conclude this from the effect which any alarm produces in causing them to display their powers, as if it was for the purpose of discovering danger. This may be observed even in the most minute ; but it is ex tremely remarkable in the larger fishes, as we formerly no ticed respecting the pilchard and the herring. Unfortu nately we can never become very intimately acquainted with this department of creation, and must, therefore, be content to draw our conclusions in the best manner that we can.
We must now recall to our readers' minds the remarks which we made at the beginning of this subject,] respect ing the phosphorescence of dead fishes. We have no doubt that the object of it is the same ; namely, to point these out as a prey to others. By this means they are not only removed, so as to prevent the inconveniences which would arise from their putrefaction, as terrestrial animals are by birds and beasts of prey, but they serve the purpose of food to numbers. It is worthy of notice, too, that this phosphorescence immediately succeeds death, while it precedes putrefaction ; so that the dead animal becomes of as much use as the living one would have been. Sure ly such a provision is not casual ; and most probably its objects are those which we have here stated. It is in the same way also that we must probably explain the desire which fishes show to follow light at night; a feeling which is turned to account by fishermen in many well known in stances, and which might probably be used still more ex tensively with advantage. That they are then in pursuit of an imaginary prey, can admit of little doubt.
Such, then, are our opinions respecting the uses of the phosphorescent property in fishes. We had imagined them new and peculiar to ourselves for some time, till we found a passage, not, however, in the writings of a natu ralist, which seems to prove that he at least, if not others in his day, had entertained something like the same no tions on this subject. In his well known collection of Poe sies, called the Mistress, Cowley compares his fair one when bathing to a luminous fish, and insinuates at the same time the purpose for which these lights are hung out. The simile is among the most outrageous ; but it will not much alarm those who are accustomed to the writings of the me taphysical. poets.