Illustrating the opposite extreme of the development of scales, we find such fishes as the bony pikes of North American lakes and rivers, the bodies of which are covered with an armor of closely fitting and overlapping scales or plates, named ganoid, from their shining appearance (Greek _ganos_, splendor). The scales of this fish are said to be employed in the manufacture of the little “mother-of-pearl” buttons, so commonly used. Many fossil fishes were also abundantly provided with these hard, bony plates; and our living sturgeons possess scales of similar nature, although in the latter fishes they do not completely cover the body. The bright silvery scales of the herring and its neighbors are thin structures, and are very easily detached from the skin; and a curious form of scale is seen in the perches; the hinder edge of each scale in the latter case being cut into comb-like teeth. In the sharks, skates, and rays, the scales are small and horny, and are often provided with little spines. If we draw our hand along the back of a dog-fish from tail to head, as when we stroke a cat’s back the wrong way, we feel numerous small projecting points, borne on the scales. The rough skin surface thus produced is frequently used under the name of “shagreen” in the manufacture of spectacle-cases and like articles, and is also employed for polishing the surface of wood. In their general shape the bodies of fishes exhibit a great compression from side to side, a rounding of the sides, and a pointing of either extremity, adapting the animals for easy progression through the water. Some fishes, such as the soles, flounders, plaice, etc., are named “flat fishes” from the great flattening exhibited by their bodies; although, at the same time, it is important to observe that these fishes are simply more compressed from side to side than their neighbors. Most persons, on looking at a sole or flounder, are apt to think that one of the flat surfaces must represent the back, and the other the under surface of the body. This idea is strengthened by the fact that the so-called back surface is dark, and the apparent under surface light in color, and because both eyes exist on the dark-colored surface. That, however, the flat surfaces are really the _sides_ of the fish may be seen by noting that on each surface a breast-fin is developed; these fins being placed invariably one on each side of the body. And while the eyes in early life are disposed one on each side of the head, in the position in which eyes are naturally situated, they are gradually brought round to one side by the bones of the head becoming curiously twisted in the course of development. Thus these fishes lie and swim on one side--that which is light-colored--and present a most singular combination of curious and abnormal features.