Page:Popular Science Monthly Volume 21.djvu/621

Rh effect is a saw-cut. It then acts as a veritable saw. But it seems absurd for an animal to carry teeth on the outside of his nose.

With another shark the tail is a weapon, as it is with the whale also. The tail of the thrasher is extremely large, and can deal severe blows. The thrashers have been known to attack the whale when the latter is at the surface. It is conjectured that the thrashers and the sword-fish form a conspiracy against the whale, and, while the latter prevent the whale from diving, the former leap out of the water and bring their huge tails down on the naked back of the whale with a tremendous slap that can be heard a long way. Probably the whale is. more frightened than hurt.

Some rays or skates have the tail long and whip-like. It is covered with sharp spines, and forms an effective instrument for either striking or grasping. These spines produce severe inflammation, and are greatly dreaded by fishermen. The larger ones are much used by savages for edging weapons. It is supposed that the whip-ray seizes an enemy, or its prey, with its tail, and kills it by the cutting spines on its tail, and by pressing it against the barbed spine situated on its back. These spines are commonly used as spear or arrow heads by the savages of the South Sea.

Some small creatures have forceps or jaws as weapons. Those of the lobster are modified feet, while those of the beetle are mouth-parts.

The most elaborate organs of defense are found in the lower forms of life. And at near the lowest point in the animal scale we find an apparatus exceedingly complex and efficient. This is the "nettling-threads," "lasso-cells," or cnidæ which give the hydra, jelly-fish, and



polyps their power of stinging. They are also possessed by the crinoids, some naked sea-snails, and some sea-worms. Like many other weapons, they are used to subdue prey as well as to repel enemies. These creatures are soft and delicate, and would seem to be the easiest food for other animals. The cnidæ are probably their only defense, but they seem quite sufficient. A chapter would be required to give a full description of these wonderful weapons. The instrument consists of a hollow filament, coiled in a sac, the whole of microscopic size. The sacs are commonly on the surface of the tentacles and other free surfaces of the body. In some species they are collected in