The Book of Household Management by Mrs. Beeton

by them in a high degree, and others much more imperfectly. Of the latter kind are the senses of touch and taste, which are believed to be very slightly developed. On the other hand, those of hearing, seeing, and smelling, are ascertained to be acute, but the first in a lesser degree than both the second and third. Their possession of an auditory organ was long doubted, and even denied by some physiologists; but it has been found placed on the sides of the skull, or in the cavity which contains the brain. It occupies a position entirely distinct and detached from the skull, and, in this respect, differs in the local disposition of the same sense in birds and quadrupeds. In some fishes, as in those of the ray kind, the organ is wholly encompassed by those parts which contain the cavity of the skull; whilst in the cod and salmon kind it is in the part within the skull. Its structure is, in every way, much more simple than that of the same sense in those animals which live entirely in the air; but there is no doubt that they have the adaptation suitable to their condition. In some genera, as in the rays, the external orifice or ear is very small, and is placed in the upper surface of the head; whilst in others there is no visible external orifice whatever. However perfect the _sight_ of fishes may be, experience has shown that this sense is of much less use to them than that of smelling, in searching for their food. The optic nerves in fishes have this peculiarity,--that they are not confounded with one another in their middle progress between their origin and their orbit. The one passes over the other without any communication; so that the nerve which comes from the left side of the brain goes distinctly to the right eye, and that which comes from the right goes distinctly to the left. In the greater part of them, the eye is covered with the same transparent skin that covers the rest of the head. The object of this arrangement, perhaps, is to defend it from the action of the water, as there are no eyelids. The globe in front is somewhat depressed, and is furnished behind with a muscle, which serves to lengthen or flatten it, according to the necessities of the animal. The crystalline humour, which in quadrupeds is flattened, is, in fishes, nearly globular. The organ of _smelling_ in fishes is large, and is endued, at its entry, with a dilating and contracting power, which is employed as the wants of the animal may require. It is mostly by the acuteness of their smell that fishes are enabled to discover their food; for their tongue is not designed for nice sensation, being of too firm a cartilaginous substance for this purpose.