sea-anemones: their weapons. 373 



The most careful observations have failed to reveal 

 a lining membrane to the cnida. I have repeatedly 

 discerned 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 ecthoreum bursts out. My 

 first supposition, reluctantly resigned, was, that some 

 such lining membrane, 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 ecthoreum^ sometimes swiftly, and sometimes more 

 deliberately. Nothing that I have seen would lead me 

 to conclude that the wall of the cnida is ciliated. 



I consider, then, that this fluid, holding organic 

 corpuscles in suspension, is endowed with a high degree 

 of expansibility ; that, in the state of repose, it is in a 

 condition of compression, by the inversion of the ectlio- 

 reum; and that, on the excitement of a suitable stimulus, 

 it forcibly exerts its expansile power, distending, and, con- 

 sequently, projecting, the tubular ecthoreum, — the only 

 part of the wall that will yield without actual rupture. 



It has been proved that the execution of these weapons 

 is as effectual as their mechanism is elaborate. The wire 

 shot with such force penetrates even to its base the tissues 

 of the living animals which the Anemone attacks ; and 

 then its barbs preclude the withdrawal of the dart. But 



