Page:Mrs Beeton's Book of Household Management.djvu/338

292 of most fish, is connected with the termination of certain nerves, and enables a fish coming into contact with any substance to feel its presence. The sense of taste is not very delicate, the tongue and palate being for the most part cartilaginous, and frequently set with teeth. Fish have no external organ of hearing, and the internal apparatus is partly free in the cavity of the skull, differing in this respect from that of birds and quadrupeds, while its structure is simpler than that of animals which live entirely in the air. 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, while in others there is no visible external orifice. The sight of fish is keen; the eye is large and flattened externally, and is furnished behind with a muscle which adjusts the focus to the requirements of the fish by lengthening or flattening the eye. It is in most cases covered with the same transparent skin which extends over the rest of the head, protecting the organ from the action of the water. The crystalline humour is almost globular. The organ of smelling is large, and consists of a double cavity lined by a mucous membrane folded into numerous plaits, into which water is admitted usually by two distinct apertures or nostrils. The nasal sacs are closed behind, and, except in the cases of the bog-fish and the mud-fish, do not, like the higher vertebrates, communicate with the throat. The sense of smell is the chief agent by which fish discover their food.

The Food of Fish.—This is almost universally found in the water. Fish are mostly carnivorous, though they seize upon almost anything that comes in their way; they even devour their own offspring, and manifest a particular predilection for living creatures. Innumerable shoals of one species pursue those of another, with a ferocity which draws them from the pole to the equator, through all the varying temperatures and depths of their boundless domain. Many species must have become extinct, were not the means of escape, the production, and the numbers greater than the dangers to which they are exposed. The smaller species are not only more numerous, but more productive than the larger, whilst their instinct leads them in search of food and safety near the shores, where, from the shallowness of the waters, many of their foes are unable to follow them.

The Fecundity of Fish is remarkable, and is especially noticeable in the sturgeon, salmon, cod, mackerel, flounder and herring, whose powers of reproduction are almost incredible. In general fish are oviparous, or egg-producing, the young being afterwards hatched; some few, like the eel and the blenny, are viviparous, and produce their young alive. The viviparous species are not so prolific. The eggs in the roe of the shark are comparatively few, and each ovum before exclusion is provided with a horny sheath furnished with cirri, or filaments, by which it moors itself to a fixed object. Reproduction is effected by the milt of the male and the roe of the female fish. The majority of