32 THE POPULAR SCIENCE MONTHLY. 



same time,, the opposite extremities of a worm. Each having swal- 

 lowed its respective half of the worm, he watched to see the result. 

 Tlie 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 

 manoeuvres of the two. The hydra inside managed to work its way 

 through the small apei-ture 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 se- 

 curely 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 veiy 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 tlie sound tissue, and the hydras generated by artificial sec 

 tions 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 ]>lant-like character 

 of the organism than for its intrinsic beauty. 



The geographical distribution of the Hydroidm 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 Tliomson, in his "Depths of the Sea" that made in the Bay 



