418 EVENINGS AT THE MICROSCOPE 



the centre of the evolved ventricose portion. But perhaps 

 the most instructive and convincing example of all was the 

 following. One of the large tangled cnidce, of Corynactis 

 viridis had shot about half of its wire with rapidity, when 

 a kind of twist, or 'kink,' occurred against the nipple of 

 the cnida, whereby the process was suddenly arrested. 

 The projectile force, however, continuing, caused the im- 

 pediment -to yield, and minute portions of the thread flew 

 out piecemeal, by fits and starts. By turning the stage- 

 screw I brought the extremity of the discharged portion 

 into view, and saw it slowly evolving, a little at a time. 

 Turning back to the cnida, I saw the kink gradually give 

 way, and the whole of the tangled wire quickly flew out 

 through the nipple. I once more moved the stage, follow- 

 ing up the ecthorceum, and presently found the true ex- 

 tremity, and a 'large portion of the wire still inverted; 

 slowly evolving, indeed, but very distinct throughout its 

 whole course, within the walls of the evolved portion. 



' ' From all these observations there cannot remain a 

 doubt of the successive eversion of the entire ecthorceum. ' ' 



You ask, What is the nature of the force by which the 

 contained thread is expelled? ''That it is a potent force 

 is obvious to any one who marks the sudden explosive 

 violence with which the nipple- like end of the cnida gives 

 way, and the contents burst forth; as also the extreme 

 rapidity with which, ordinarily, the whole length is 

 evolved. A curious example of this force once excited 

 my admiration. The ecthorceum from a cnida of Gorynactis 

 viridis was in course of rapid evolution, when the tip came 

 full against the side of another cnida already emptied. 

 The evolution was momentarily arrested, but the wall of 

 the empty capsule presently was seen to bend inward, 



