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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



beings are ushered into the field of active life to 

 take part in carrying on the life of the species, 

 just as the process of nutrition made good the 

 wants and supplied the exigencies of the single 

 form. 



The Harveian motto, " omne ex ow," holds 

 good in the case of the hydra, inasmuch as we find 

 that the animal in summer more especially may 

 be seen to produce eggs, from which, through a 

 process of regular and defined development, new 

 hydra? are produced. But we may concern our- 

 selves less with this normal phase of develop- 

 ment than with certain strange and out-of-the- 

 way features which our polyp may be observed 

 to exhibit. There are very few persons outside 

 the ranks of biologists who would be inclined to 

 associate a veritable process of " budding" with 

 the functions of an animal organism. Yet in the 

 hydra, in a large number of its neighbors, and in 

 a few other groups of the animal world, a verita- 

 ble process of this nature occurs, whereby from 

 a parent-body certain portions are gradually bud- 

 ded out to assume in due time the form and like- 

 ness of the being which has produced them. 



Thus, when the hydra is well nourished, little 

 projections may be observed to sprout from the 

 side of the body. As these projections increase 

 in size, each is seen gradually to develop a mouth 

 and little tentacles at its free end, and in due 

 time presents us with the spectacle of a young 

 hydra, which has budded from the parent, to 

 which, save in size, it bears a close resemblance. 

 Sometimes, also, it so happens that this young 

 bud grows and multiplies like its parent, and 

 produces a bud in its turn. So that we meet, in 

 such a case, with a veritable genealogical tree, 

 presenting us with three generations of hydra, 

 adhering to each other, and connected by the 

 closest ties of blood-relationship. Not only, 

 therefore, is our hydra colored like a plant : it 

 also imitates the plant-creation in certain aspects 

 of its life-history, and by the process of budding 

 converts itself from a single into a compound 

 animal. While the young buds remain attached 

 to the parent, free and perfect communication 

 exists between the simple body-cavities of the 

 connected individuals, and the compound organ- 

 ism is thus nourished by as many mouths as 

 there are animals in the colony. But this con- 

 nected and compound state is not permanent in 

 the hydra; although, as seen in the zoophytes, 

 it presents us with a complicated and enduring 

 fabric, numbering, it may be, many hundreds of 

 included animals which have been produced by a 

 process of budding. Sooner or later the young 



hydra-buds will break contact with the parent- < 

 body, and will float away through the surrounding 

 water on their way to root themselves to fixed 

 objects, and to begin life on their own account. 



More astonishing by far, however, is it to find 

 that we possess the means for propagating hydra; 

 at will. We may actually imitate the experiment 

 performed of old by that redoubtable demigod 

 Hercules, since by the artificial division of one 

 polyp we may give origin to new beings, and 

 may multiply the species through the destruction 

 of a single individuality. These curious results, 

 also obtained by experimentation on the sea- 

 anemones, were first made known to the world 

 at large by Trembley, an Englishman, who was 

 tutor to the sons of Count Bentinck, and who 

 also, while resident at Geneva about the middle 

 of the last century, contrived to find time and 

 opportunity for close observation of those polyps. 

 In 1744 Trembley published his memoir on the 

 hydra;, and we shall leave the ingenious naturalist 

 to detail in his own language the method and re- 

 sults of his experiments. Surprised at the cu- 

 rious life-history and plasticity of these creatures 

 under almost every condition, Trembley resolved 

 to ascertain if the reproductive powers of hydra; 

 were further allied to those of plants in their 

 ability to reproduce their like by being divided 

 into "slips." Having divided a hydra crosswise 

 and nearer to the mouth than to the root-ex- 

 tremity, he put the two parts into a flat glass 

 which contained water four or five lines in depth, 

 and in such a manner that each portion of the 

 polyp could be easily observed through a strong 

 magnifying-glass. " On the morning of the day 

 after having cut the polyp, it seemed to me that 

 on the edges of the second part, which had 

 neither head nor arms, three small points were 

 issuing from these edges. This surprised me ex- 

 tremely, and I waited with impatience for the 

 moment when I could clearly ascertain what they 

 were. Next day they were sufficiently developed 

 to leave no doubt on my mind that they were 

 true arms. The following day two new arms 

 made their appearance, and some days after a 

 third appeared, and I now could trace no differ- 

 ence between the first and second half of the 

 polyp which I had cut." 



Experimenters since Trembley's time, but fol- 

 lowing in the track of that ingenious observer, 

 have cut and divided the hydra in almost every 

 possible fashion, with the result of finding that 

 the polyp possesses an unlimited power, not only 

 of resisting injuries — the least of which would 

 be sufficient to insure the death of any ordinary 



