872 EVENINGS AT THE MICROSCOPE. 



was the following. One of the large tangled cnidm 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 sud- 

 denly arrested. The projectile force, however, continuing, 

 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 pre- 

 sently found the true extremity, 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 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 Corynactis 

 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. 



The most careful observations have failed to reveal a 

 lining membrane to the cnida. I have repeatedly dis- 



