We now come to the fishes of the sea; and at the head of these we may place the sharks. These savage and voracious creatures are found in all oceans, the larger ones wandering very widely, while the smaller ones are restricted to limited parts of the sea. Among the latter are the various small sharks called dogfish, from eighteen inches to six feet long, found on both sides of the North Atlantic. Though small, and harmless to man, the dogfish really is a shark, and for its size is very formidable, being able easily to fight and kill fishes quite as large as itself. It is called the dogfish because it follows shoals of fish in the water, just as a wild dog will follow the animals on which it preys upon dry land. When you are staying at the seaside you may sometimes find the dead body of a dogfish lying on the beach, where it has been flung by a very high wave. And you will notice how coarse and rough its skin is. This skin is often used for covering the handles of swords, as it gives such an excellent grip; and also for putting on the sides of match-boxes instead of sandpaper. But even if you do not find the dogfish itself lying on the beach, you may often find its eggs, which are very curious little objects. They are something like oblong horny purses, of a yellowish-brown color, with a long twisted appendage at each corner, very much like the tendrils of a vine. By means of these the egg is anchored down to the weeds at the bottom of the sea, and they hold so firmly that they are hardly ever torn away, except during a violent storm. At each end of this singular egg is a narrow slit, through which water can pass to the gills of the little fish which is lying inside it. And one end of the egg is made in such a manner that when the fish is ready to hatch it can easily push its way out. THE BLUE SHARK A much larger and more dangerous fish, which often visits northern seas, is the blue shark, which sometimes grows to a length of fifteen or sixteen feet. It does not often attack human beings, however, but is very destructive in our fisheries, snatching away fishes which have been hooked, and even swimming along the outside of the nets as they are being drawn in, and biting great holes through them, in order to get at the pilchards or herrings within. So the fishermen always kill a blue shark if they have the chance of doing so, and sometimes destroy eight or ten in a single day. But it is not very easily caught, for if it is hooked it will often bite the line asunder, and if it cannot do this will roll round and round in the water coiling the line round its body, when it will snap with a sudden jerk. Even when it is caught, the blue shark is not killed without much difficulty, for it thrashes its great powerful tail about in such a manner that it cannot be approached without danger. So the first thing that the fishermen always try to do when it is captured is to chop off its tail with an ax.