Such, then, is our little minnow, and the different parts of his body are supported by a slender bony-jointed backbone, with ribs growing from it, supporting a strong mass of flesh on his sides. He is a delicate tender creature, but is protected and buoyed up by the water, out of which he never attempts to go. The thin, rounded, transparent scales which cover his body, growing out of little pockets in his skin, just like our nails on the tips of our fingers, protect this skin from the water and from rough treatment; while they themselves are kept soft by a slimy fluid which oozes out from under them, and especially through the dark line of larger scales (_ms._ Fig. 4) running along his body. * * * * * Now the minnow is a bony fish, and from it we can learn very fairly what bony or modern fishes are like. But these fish were not the founders of the race; long before they existed there was another very ancient group of fishes in the world, which were in many ways more like the lancelet and the lamprey; and to find such descendants of this ancient group as are now living we must leave the river and find our way into the open sea. If we do this, we shall travel not many miles from the shore in summer, wending our way through shrimps and lobsters, gurnards, cod-fish, soles, and turbot, before we may chance to come across a great Blue shark, with his slaty-coloured back and fins, swimming heavily but strongly through the water, and turning sharply from time to time to seize a passing fish, his white belly gleaming like a flash of light as it comes uppermost, and then disappearing again in the dark water. “His jaws horrific, armed with threefold fate, Here dwells the direful shark.” Or if this formidable monster does not happen to be in the neighbourhood another kind, the Dogfish, may cross our path, perhaps the Smooth hound, crushing the crabs and lobsters in his tooth-lined mouth, or the Rough hound fastening her purse-like egg to the seaweed by its long string-like tendrils; or, farther out still, we may perhaps see the Thresher shark lashing the water with his long pointed tail, to drive the frightened fish within his reach; or, if we were off the west coast of Ireland, the huge but harmless Basking shark might be floating calmly by in the warm sunshine. For sharks travel all over the ocean, and though they prefer the warm seas, where they sometimes reach a size of forty feet long and more, yet many of the smaller kinds visit our coasts in summer. [Illustration: Fig. 5. The Blue Shark[10] (_from Brehm_). To show the five slits in the neck, the uneven tail, and the mouth opening under the pointed snout.]