A STUDY OF LOWER LIFE. 



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 hydra 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 

 more delicate nature we shall have 

 formed a broad but accurate idea of the physical constitution 



FIG. 2. Diagrammatic 

 section of hydra. 



