SEA-ANEMONES: THEIR WEAPONS -4.19. _ 



and suddenly to give way, the ecthorceum forcing itself 

 in, and shooting round and round the interior of the cnida. 



"The most careful observations have failed to reveal 

 a lining membrane to the cnida. I have repeatedly dis- 

 cerned a double outline to the walls themselves, the optical 

 expression of their diameter; but have never detected 

 any, even the least, appearance of any tissue starting from 

 the walls, as the ecthorceum bursts out. My first supposi- 

 tion, reluctantly resigned, was that some such lining mem- 

 brane, of high contractile power, lessened, on irritation, 

 the volume of the cavity, and forced out the wire. 



"The cnida is filled, however, with a fluid. This is 

 very distinctly seen occupying the cavity when, from any 

 impediment, such as above described, the wire flies out 

 fitfully; waves, and similar motions, passing from wall to 

 wall. Sometimes, even before any portion of the wire 

 has escaped, the whole mass of tangled coils is seen to 

 move irregularly from side to side, within the capsule, 

 from the operation of some intestine cause. The emission 

 itself is a process of injection; for I have many times seen 

 floating atoms driven forcibly along the interior of the 

 ecthorceum, sometimes swiftly, and sometimes more delib- 

 erately. Nothing that I have seen would lead me to con- 

 clude that the wall of the cnida is ciliated. 



"I consider, then, that this fluid, holding organic cor- 

 puscles in suspension, is endowed with a high degree of 

 expansibility: that, in the state of repose, it is in a condi- 

 tion of compression, by the inversion of the ecthorceum; 

 and that, on the excitement of a suitable stimulus, it for- 

 cibly exerts its expansile power, distending and, conse- 

 quently, projecting, the tubular ecthorceum the only part 

 of the wall that will yield without actual rupture." 



