2 
Huxley on Lacinularia socialis. 
ramified animals like the freshwater Polyzoa, to which, at 
first sight, they have no small resemblance, but may be truly 
called compound animals, since each of the Lacinulari(E is a 
separate individual, which at one time swam about freely by 
itself,* which has voluntarily united itself with its fellows, 
and has taken its share in throwing out the gelatinous sub- 
stance which connects them into a whole. 
Each Lacinularia (PI. T. fig. 1) has an elongated conical 
body, whose outer extremity is considerably the wider, and 
whose inner smaller end is truncated, and serves as a sucker 
or means of attachment to the stem on which the whole mass 
is seated ; the outer third or fourth of the body contains the 
viscera, nothing but the muscular cords extending into the 
inner narrow elongated part of the animal. During con- 
traction the latter portion is thrown into sharp folds, while 
the visceral portion presents only three or four faint transverse 
constrictions. 
When the Rotifer is in a state of expansion and activity, 
its outer extremity is terminated by a large horseshoe-shaped 
wheel-organ, or " trochal disc " (figs. 2, 3), connected with 
the body by a narrowed neck. When contracted and at rest, 
the whole of this apparatus is drawn in, and the body takes 
on a more pyriform appearance (fig, 5). 
The mouth lies in the notch of the trochal disc (fig. 4 d) ; the 
anus is placed on the opposite side, at the lower part of the 
visceral portion of the animal (K). 
Anatomy of Lacinularia. — I will now proceed to describe 
the various organs of the animal more minutely. 
The " trochal disc " is, as I have said, wide and horseshoe- 
shaped. It is seen in profile at figs. 1 and 2 ; from above 
at fig. 3. Its edges are richly beset with large cilia, which 
present a very beautiful wheel-like movement. 
Ehrenberg says that the ciliary organ is "as in Megalo- 
trocha^^ and in this he describes the disc as having a simple 
ciliated edge. I have not examined Megalotrocha, but I can 
say most decidedly that such is not the structure of La- 
cinularia.'\ 
In fact, the edge of the disc has a considerable thickness, 
and presents two always distinct margins — an upper {p) and 
* Or rather had the power of swimming about freely ; for it does not 
appear that the young Lacinularice ever do leave the gelatinous envelope 
of the parent mass, unless aggregated together. 
t Ley dig (Ziir Anatomie und Entwickelungs-geschichte der Lacinu- 
laria socialis — Siehold and Kolliker's Zeitschrift for February, 1852) says 
that "an elevated ridge runs along the lower surface of the wheel organ, 
not far from and parallel to its margin, whence there is a double edge and 
a groove, in which alone ciliary motion is observed." 
