Fig. 20.—Lassos or weapons of a jellyfish.
The weapons are known as lassos (Fig. 20). Under the microscope the tentacles appear to be filled with little cells or oblong objects, which when examined are found to be capsules (C) resembling long glasslike bodies in which is coiled a thread. This latter is a miniature javelin, and when the tentacle of a jellyfish is seized by a fish or an enemy, tens of thousands of these cells literally explode (D) and the javelin springs out like a Jack-in-the-box (A) and penetrates the intruder. With many jellyfishes the effect of this bombardment is a stinging sensation. It paralyzes small fishes which, when benumbed, are lifted up by the tentacles and eaten.
Fig. 21.—Jellyfish and young (Aurelia).
The jellies develop in various ways. In Figure 21 we see a common and very beautiful form resting on the rocks. Near by are various little plantlike creatures, the young jellies, which undergo a remarkable series of changes in their growth from the egg to the adult form. Minute eggs are deposited in the autumn, which drop into the crevices of the rocks and soon change to pear-shaped objects which attach themselves to the bottom. Each little jelly pear (Fig. 22) divides after a while until it looks like a pile of platters one upon the other. The upper one dies, and the rest break away, each becoming a separate jellyfish, which ultimately grows to be a giant.
Fig. 22.—The development of a jellyfish.
The story of the growth and development of these little jellies is one of the most marvelous pages in the history of nature. In some forms the father and son are entirely different, and it is only the father and grandson that resemble each other. Not only this, the father is a seeming plant, while the son is a free-swimming jellyfish of great beauty. The seeming plant is in reality a hydroid community. The buds are immature jellyfishes which finally break away and assume the typical jellylike form, free swimmers bearing not the slightest resemblance to the parent. This jelly deposits eggs which attach themselves to the bottom and become not jellies but the shrublike form. Hence it is the parent and its grandchildren that bear a close resemblance to one another.
