INTRODUCTION. 
XXXV 
have actually seen the unevolved portion of the ecthorcBum 
running out through 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 
cnidae of Corynac.tis viridis had shot about half of its wire 
Avith rapidity, Avhen 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 impediment to yield, and minute portions of the 
thread flew out, piecemeal, by fits and starts. By turning 
the stage-screw 1 brought the extremity of the discharged 
portion into view, and saw it sloAvly evolving, a little at a 
time. Tm'iiing back to the cnida I saw the kink gradually 
give way, and the whole of the tangled wire quickly fleAv 
out through the nipple. I once more moved the stage, fol- 
lowing up the ecthor(Bum, and presently found the true 
extremity, and a large portion of the wire still inverted ; 
slowly evolving indeed, but very distinct throughout its 
whole coiu’se, within the walls of the evolved portion 
(fig. 8). 
From all these observations, there cannot remain a doubt 
of the successive eversion of the entire ectliormum. It may 
be asked. 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 ecthorccuni trom 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 
Avas momentarily arrested, but the wall of the empty 
capsule presently Avas seen to bend iiiAvard, 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 themsch'es — the 
optical expression of their ^ diameter ; but liavc ncA’cr 
detected any, even the least, appearance of any tissue 
starting from the walls, as the ecthoraeum bursts out. My 
first supposition, reluctantly resigned, Avas, that some such 
