Page:Popular Science Monthly Volume 21.djvu/622

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606
THE POPULAR SCIENCE MONTHLY.

like magazines which are shot out of the body-walls. Upon irritation this hollow thread is thrown out of the sac to a great length, by eversion. It is turned inside out, and then exposes a barbed surface. They penetrate the soft tissues of the animal attacked, and convey a poison fatal to small animals. Any bather who has ever been stung by a jelly-fish can give a satisfactory account of the effect of these weapons. There is no doubt that a man would be completely and quickly paralyzed if entangled, in a nude state, among the tentacles of the larger jelly-fishes.

The stings of insects are more familiar, but still very wonderful. In the sting of the honey-bee "we see an apparatus beautifully contrived to enter the flesh of an enemy; two spears finely pointed, sharp-edged, and saw-toothed, adapted for piercing, cutting, and tearing; the reversed direction of the teeth gives the weapon a hold on the flesh, and prevents it from being readily drawn out. Here is an elaborate store of power for the jactation of the javelins, in the numerous

PSM V21 D622 Barbed case of everted nettling thread.jpg
Fig. 10.—Barbed Case of Everted Settling-Thread. (After Gosse.)

muscular bands; here is a provision made for the precision of the impulse; and, finally, here is a polished sheath for the reception of the weapons and their preservation when not in actual use. All this is perfect; but something still was wanting to render the weapons effective, and that something your experience has proved to be supplied." This is the poison, which has also a complex apparatus for its secretion and ejection. This sting is a modified ovipositor, and possessed only by the females, or neuters, which are undeveloped females. The male insect is always a mild and inoffensive creature.

Scorpion-stings are similar to those of insects in position and use, but are unlike in origin and development.

The poison-fangs of venomous snakes are modified teeth. They are so attached that when not in use they lie in a fold in the upper jaw. The poisonous snakes have broad heads, on account of the muscles which control the fangs and the large glands which secrete the venom. The latter is a sort of saliva, probably charged with fermenting organisms, which are harmless in the food-canal, but which in the blood multiply with amazing rapidity. The poison is conveyed to the wound by a groove in the side of the fang.

The fangs of spiders represent the antennæ of insects. They are tubular, for conveying venom, and jointed. The point or terminal joint when not in use shuts into the basal joint, like the blade of a