XXXll 
INTRODUCTION. 
error of another kind I fell into, in supposing that the 
triple screw of the wire in C. Smith ii was a series of 
imbricate plates : the structure of the armature is tlie same 
in all cases (■s\dth the variations in detail that I have just 
indicated) ; and the structure is, I am now well assm-ed, 
a spiral thickened band, running round the wall of the 
ecthoraum on its exterior surface. I have been able, when 
examining such large forms as those of Corynactis and 
Caryo^hyllia, with a power of 750 diameters, to follow the 
course of the screw, as it alternately approached and receded 
from the eye, by altering the focus of the objective, so as 
to bring each part successively into the sphere of vision. 
These thickened spiral bands afford an insertion for a 
series of firm bristles, which appear to have a broad base 
and to taper to a point. Tlieir length I cannot determin- 
ately indicate, but I have traced it to an extent which 
considerably exceeds the diameter of the ecthor£eum. These 
barbed bristles I denominate fa. (See fig. 7,p.) _ 
The number of yterygia appears to vary within slight 
limits. As well as I have been able to make out, there are 
but eight in a single volution of the one-banded strebJa in 
T. crass icor Ills ; while in the more complex screws of S. 
parasitica, Cor. viridis, and Cary. Smithii there appear to 
be twelve in each volution. 
The barbs, when they first appear, invariably project in 
a diagonal direction from the ectliorcBum ; and sometimes 
they maintain this posture ; but more commonly, either in 
an instant, or slowly and gradually, they assume a reverted 
direction. 
From some delicate observations, made with a very good 
light, I have reason to conclude that the strebla, and even 
the pterygia, are continued on the attenuated portion of the 
ecthormiin, perhaps throughout its length. In Corynactis 
and Caryophyllia I have succeeded in tracing them up a 
considerable distance. In the latter I saw the continuation 
of all these bands, with their bristles; but the angle of 
inclination had become nearly twice as acute as before, 
being only 22° from the axis. The appearance of the 
attenuate portion, as also of the base of the ventricose part, 
is exactly that of a three-sided wire, twisted on itself ; the 
barbs projecting from the angles. 
(2.) Tangled Cnidce {Cnidce glomiferce). This form is 
very generally distributed, and is mingled with the former 
