Leisure-time studies, chiefly biological : a series of essays and lectures / by Andrew Wilson.

  • Wilson, Andrew, 1852-1912.
Date:
1884
Catalogue details

Licence: Public Domain Mark

Credit: Leisure-time studies, chiefly biological : a series of essays and lectures / by Andrew Wilson. Source: Wellcome Collection.

    71/442 (page 49)
    consideration of the structure and functions of these thread- cells clearly indicates their offensive nature. Each may in fact be regarded as representing a miniature poison- apparatus ; the “ thread ” being the dart or sting, and the fluid constituting the venom. The prey of these polypes has little chance of escape from the attack of these cells; since, wounded by the threads, which doubtless become attached to its body by the hooks, and poisoned by the fluid, even animals of tolerably large size when compared with the hydra, may be seen to succumb to its attack. The polypes are thus noted to be singularly well provided as regards offensive apparatus, the particular form of action of which reminds one, in some degree, of the famous “ lasso ” of Western nations. And it is, at the same time, interesting to note that thread-cells of essentially similar nature to those found in hydrae confer on the jelly-fishes and allied forms the stinging powers which render these beings the terror of tender-skinned bathers. The internal structure of our polype is of the simplest possible description. It may seem strange to talk of an animal body which lives and grows without any of the structures or ma- chinery we are accustomed to associate with higher animals. Yet the hydra .exemplifies the former condition, since we might accurately enough describe its body as consisting of a simple tube (Fig. 2), the interior of which contains no organs of any kind, and which com- municates with the outer world through the mouth (d). If we further suppose that the walls of this tubular body are composed of two closely applied layers or membranes (a, b)—the outer some- what dense and tough, and the inner of Fig. ^.-Diagrammatic more delicate nature—we shall have section of hydra. formed a broad but accurate idea of the physical constitution