Page:Popular Science Monthly Volume 51.djvu/536

522 darts. Then "begins a tussle which generally ends in the captive being conveyed to the mouth. Occasionally some strong swimmer may get away, but, unless he is armor-plated, he has but little chance of his life, for a poisoned dart is most probably imbedded in his body. Sometimes a victim is very troublesome, and, in order to get it safely into its mouth, the tentacle itself must also be partially ingulfed, and it remains so until the morsel is quiet, and even until digestion has begun. As the food is drawn in, you can see the body swell, and in some cases become quite pear-shaped. After a while the swelling subsides, and, after all the useful part of the food has been extracted, the rest is ejected at the same place at which it entered. It is most interesting to watch the instinctive motions of this creature, which is totally destitute of what we should call brain.

Hitherto we have spoken only of a single individual, but we must now notice a startling fact. The hydra is multiplied according to the usual law—by eggs, it is true; but also in another way. You can not examine a group in summer time without finding that they "bud." You see the trunk of one bearing a second, perfect in every respect, except that it is connected with its parent, instead of resting on a foreign substance. It has sprouted out from the parent stock, like a sucker from a tree. It may break off after a while and seek an independent resting place, or it may send out a bud from its own stem, which in its turn may do the same, and all may remain attached for some time. While this connection lasts, each member of the compound body forages at his own "will," but the tubes of each connect with the trunk of the next, and so with the parent stomach. Thus they form a colony in which each member helps to maintain every other member by his labor. A sight of such a colony of hydras, the working of which is visible to the naked eye, helps one to understand many other similar forms of animal life—as, for instance, the corals, which form colonies by budding. As many as four generations of hydras have been seen on one stem, so that there is some reason for likening such a community to "a living genealogical tree."

By a number of experiments with which some of us will scarcely sympathize, Trembley and those who have repeated his investigations have brought out many astounding facts about these animals. If you cut one in two across the trunk, the upper part floats off and resumes its voracious habit in a new locality; while the lower portion remains, develops a new set of tentacles, and goes on just the same as if nothing had happened. Nay, you may cut a hydra into five or six pieces, and each will make a separate animal. If one is divided into two vertically, the two halves close up, and again you have two individuals. Trembley