372 EVENINGS AT THE MICROSCOPE. 



the centre of the evolved ventricose portion. But per- 

 haps the most instructive and convincing example of all 

 was the following. One of the large tangled cnidce of 

 Cori/nactis 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, con- 

 tinuing, caused the impediment 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, following up the 

 ecthoreum, and presently found the true extremity, and 

 a large portion of the wire, still inverted ; slowly evolv- 

 ing, 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 evolution of the entire ecthoreum. 



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 ex- 

 treme rapidity with which, ordinarily, the whole length is 

 evolved. A curious example of this force once excited 

 my admiration. The ecthoreum from a cnida of Cory- 

 nactis 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 and suddenly to give way, the ecthoreum forcing 

 itself in, and shooting round and round the interior of 

 the cnida. 



