SEA- ANEMONES : THEIE WEAPONS. 419 



becoming involved in contortions more and more intri- 

 cate, as it fills up the posterior moiety of the cavity. 

 The fusiform chamber appears to be marked on its 

 inner surface with regularly recurring serrations, 

 which are the optical expression of that peculiar arma 

 ture to be described presently. 



" Under the stimulus of pressure when subjected to 

 microscopical examination, and doubtless under ner- 

 vous stimulus, subject to the control of the "jviHj during 

 the natural exercise of the animal's functions — the 

 enidm suddenly emit their contents with great force, 

 in a regular and prescribed manner. It must not be 

 supposed, however, that the pressure spoken of is the 

 immediate mechanical cause of the emission ; the con- 

 tact of the glass-plates of the compressorium is never 

 so absolute as to exert the least direct force upon the 

 walls of the capsule itself; but the disturbance pro- 

 duced by the compression of the surrounding tissues 

 excites an irritability, which evidently resides in a 

 very high degree in the interior of the cnidos ; and 

 the projection of the contents is the result of a vital 

 force. 



" In general, the eye can scarcely, or not at all, 

 follow the lightning-like rapidity with which the 

 chamber and its twining thread are shot forth from 

 the larger end of the cnidce. Eut sometimes impedi- 

 ments delay the emission, or allow it to proceed only 

 in a fitful manner — a minute portion at a time ; and 

 sometimes, from the resistance of friction (as against 

 the glass-plate of the compressorium), the elongation 

 of the thread proceeds evenly, but so slowly as to be 

 watched with the utmost ease ; and sometimes the 

 process which has reached a certain point normally. 



