Page:Natural History, Fishes.djvu/21

Rh commonly overlapping. "By maceration in water, scales exhibit a series of laminæ, the smallest in size having been the first produced; they resemble a cone, the apex of which is outwards, the smallest being in the centre; hence

the appearance of numerous concentric lines, all of the same shape, which mark the growth."

Along each side, in most fishes, may be observed a line, known as the lateral line, formed by scales of peculiar form. They are commonly more bony than the other scales, and are pierced by a tubular orifice for the escape of a mucous secretion, which is poured out from glands beneath, and thus flows over the body for the double purpose of protecting the skin from the macerating influence of the surrounding water, and of diminishing friction in swimming.

The organs of motion in this Class are the fins. They generally take the form of a delicate