Huxley on Lacinularia socialis. 
7 
Each of these bodies was along cilium (l-1400th of an inch), 
attached by one extremity to the side of the vessel, and by the 
other vibrating with a quick undalatory motion in its cavity 
(fig. 8). As Siebold remarks, it gives rise to an appearance 
singularly like that of a flickering flame. 
T particularly endeavoured to find any appearance of an 
opening near the vibratile cilium, but never succeeded, and 
several times I thought I could distinctly observe that no such 
aperture existed. Animals that have been kept for some days 
in a limited amount of water are especially fit for these re- 
searches. They seem to become, in a manner, dropsical, and 
the water-vessels partake in the general dilatation. 
The " band " (fig. 7) which accompanies the vessel ap- 
peared to me to consist merely of contractile substance, and to 
serve as a mechanical support to the vessel. It terminates 
above, in a mass of similar substance, containing vacuolae, 
attached to the upper plate of the trochal disc. I shall refer 
to this and similar structures below. 
I examined these structures so frequently that I have no 
doubt that the account I have given is essentially accurate,* 
and I am strengthened in this opinion by the account and 
figure of the corresponding vessels in Mesostomum given by 
Dr. Max Schulze, in his very beautiful monograph upon the 
Turhellaria (Beitrage zur Naturgeschichte d. Turbellarien). 
Through these the transition to the richly ciliated water- 
vessels of the Naidae, &c., is easy enough. 
Vacuolar Thickenings. — (figs. 2, 3 r). Under this head I in- 
clude a series of structures of, as I believe, precisely similar 
nature, which, on Professor Ehrenberg's principles of interpre- 
tation, have done duty as ganglia, testes, &c., in short, have 
taken the place of any organ that happened to be missing. 
In various parts of the body the parietes have become 
locally thickened, and the prominences thus formed have 
* Leydig's careful description coincides in all essential points with that 
given alDove. He particularly notices the fitness of Lacinu.lari^ that have 
been imprisoned for some time, for the examination of the water-vascular 
system. 
The only discrepancy of importance in Leydig's account is — firstly, that 
he considers what I have called the " vacuolar thickening on each side of 
the pharyngeal mass," and what Ehrenberg calls a nervous centre, to be 
formed by convolutions of the water-vessel itself ; and secondly, that he 
describes a cloacal vesicle as in other Rotifera. I looked particularly for 
such a vesicle, but could never see any ; in some cases, indeed, I could 
trace the water-vessels distinct from one another, close to the anus. 
Beyond these particular cases, however, I will by no means venture to 
contradict so accurate an observer as M. Leydig. 
Leydig does not seem to have noticed the transverse anastomosing vessel 
over the pharynx. 
