Page:Popular Science Monthly Volume 8.djvu/42

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32
THE POPULAR SCIENCE MONTHLY.

same time, the opposite extremities of a worm. Each having swallowed its respective half of the worm, he watched to see the result. The worm would not yield to the force of circumstances; and break, and the problem looked a difficult one of solution. The larger hydra, however, proved itself superior to circumstances, it quietly swallowed worm, antagonist, and all; and, after having sucked out the worm, disgorged his dinnerless foe!

Trembley tried the experiment, already alluded to, of turning one inside out, and fastening it in that position. The domestic economy did not appear to be at all disturbed; the little creature eating with as much relish, and digesting with as much ease, to all appearance, as in its normal position. He inserted one hydra within the cavity of another, and fastened them with a bristle which was run through both. Returning after a short absence he found them strung, side by side, upon the bristle. He repeated the experiment and watched the manœuvres of the two. The hydra inside managed to work its way through the small aperture made in the side of its neighbor by the bristle, and soon occupied the position he had before observed, side by side with its companion on the bristle. He then turned one of them inside out, inserted it in that position, and fastened them securely together. Soon the pair, finding that there was no help for it, philosophically yielded, and united their fortunes; the inner one of the couple providing nourishment for them both. They seemed to live quite comfortably, on these very close terms of intimacy, for some time.

Hydras generate in summer by buds, which grow to maturity and are then sloughed off. These young buds often produce others before they separate from the parent stem, and they others again; so that there are sometimes twenty generations produced in a month's time. In autumn oviform gemmules are extruded, lie quiescent till spring, and are then developed. Any number of artificial sections may be made, and from each a perfect animal will be developed. Wherever a wound or cut has been made, buds sprout more quickly than from the sound tissue, and the hydras generated by artificial sections are more prolific than those generated in the ordinary way. The sprouting, as may be seen in the plate (Fig. 12), takes place from any portion of the body. The leaves, flowers, and stems, of this specimen of Hydra vulgaris, together form the hydrasoma. This specimen was selected more to illustrate the plant-like character of the organism than for its intrinsic beauty.

The geographical distribution of the Hydroidæ has not yet been determined; but, like other low forms of life, we find them spreading over vast areas of space, and extending back through uncounted ages of time. We have already spoken of their distribution in depth. A well-defined specimen was taken up in the deepest cast recorded by Wyville Thomson, in his "Depths of the Sea"—that made in the Bay