This is a curious animal, for the male has a very long straight tusk projecting from one side of its upper jaw. This tusk is often as much as seven or eight feet in length, and the ivory of which it is made is twisted round and round in a spiral from base to tip. In former days this tusk was thought to be the horn of the unicorn, and the narwhal is often known as the sea-unicorn. In reality, this tusk is the left-hand upper "eye" tooth of the animal, that on the right-hand side being very small and completely buried in the bone of the jaw. Now and then, however, both teeth are developed, and a narwhal was once killed which had one tusk seven feet five inches long and the other seven feet. There are no other teeth in the mouth, and the female animal has no tusks at all. Now what is the use of this singular weapon? Two or three answers have been given to this question. Some people have supposed, for example, that it is used in spearing fish, or in digging up buried mollusks from the mud at the bottom of the sea. But the female narwhals require food just as much as the males do; how is it that they are not provided with tusks also? Other people have thought that when the winter is very severe, and the ice on the surface of the sea is very thick, the animal could bore a hole through it with its tusk, and so be able to breathe. But then again, female narwhals require air just as they require food. So this suggestion will not do either. The only explanation we can really give is that the narwhal's tusk is a weapon used in fighting, just like the antlers of the male deer. At any rate, narwhals have several times been seen as they were taking part in a kind of make-believe battle, and striking and clashing their tusks together just as though they were fencing with swords. And when they are fighting in earnest they must be able to use their long spears with terrible effect, for several times a narwhal has charged a ship, and driven its tusk so deeply into her timbers that it was quite unable to withdraw it. The ivory of which this weapon is made is of very fine quality. But as the tusk is hollow for the greater part of its length it is not very valuable. Narwhals are only found in the half-frozen seas of the far north, where they are sometimes seen swimming side by side together in large companies. They grow to a length of twelve feet or over, and are dark gray in color on the upper part of the body, and white underneath, the back and sides being more or less mottled with gray. THE WHITE WHALE