312 REPORT—15850. 
with the peculiar secretion of the gastric walls, and soon assumes a rich brown 
colour. After having thus undergone for some time the action of the stomach, 
the alimentary matter is delivered by degrees into the intestine, where it 
accumulates in the wide pyloric extremity of this tube. After continuing 
here for a while in a state of rest, and probably yielding to the absorbent 
tissues its remaining nutritious elements, portions in the form of roundish 
pellets become separated at intervals from the mass, and are slowly propelled 
along the tube towards the anus, where, having arrived, they are suddenly 
ejected into the surrounding water and rapidly whirled away by the tentacu- 
lar currents. It was these excrementitious pellets that Turpin mistook for 
unarmed ova in Cristatella. 
C. Organs of Respiration and Circulation—Upon the tentacular crown 
and the walls of the perigastric space would seem, among the Polyzoa, chiefly 
to devolve the function of bringing under the influence of the aérating 
medium the nutritious fluid of their tissues. 
The tentacular crown of a Polyzoon consists of two portions, namely, first, 
a sort of stage or dise (the lophophore) which surrounds the mouth; and 
secondly, of a series of ¢entacula which are borne in an uninterrupted series 
round the margin of the lophophore. The lophophore is throughout almost 
the entire class of an orbicular figure; but in the freshwater genera Crista- 
tella, Lophopus, Plumatella and Alcyonella, its posterior margin, or that 
which corresponds to the side of the rectum, is prolonged into two long tri- 
angular lobes or arms, so as to cause the lophophore in these genera to pre- 
sent the form of a deep crescent, round whose entire margin the tentacula 
are borne in one continuous series. This condition of the lophophore is 
found in no marine species. In /’redericella the arms of the crescent are 
obsolete, and the lophophere here may, on a superficial view, appear orbicu- 
lar; but a careful examination will render manifest its departure from the 
orbicular form, the side corresponding to the arms of the crescent being 
slightly prolonged obliquely upwards; a similar tendency to assume a bi- 
lateral form may also be observed, as Van Beneden* has already pointed 
out in certain marine genera. Paludicella is the only freshwater genus in 
whose lophophore not the slightest trace of bilaterality can be detected. The 
lophophore in all the genera forms the roof of the perigastric space ; in the 
species with crescentic lophophores, the arms of the crescent are tubular and 
open into this space; the interior of the arms is clothed with vibratile cilia. 
The tentacula are tubular, closed at their free extremity, and opening by 
the opposite through the lophophore into the perigastric space ; in all the 
Polyzoa they are armed upon their opposed sides with vibratile cilia, arranged 
in a single series, and vibrating towards the remote extremity of the tentacle 
upon one side, and towards the base on the other. In Fredericelia I have suc- 
ceeded in detecting two very distinct layers entering into the structure of the 
tentacula, a condition which I have also made out, though not so evidently 
in other genera, and which is in all probability common to the whole class. 
The external layer consists of rounded cells filled with a colourless fluid, and 
often presenting a bright nucleus. Some of those cells which lie upon the 
back of the tentacle become in certain genera enlarged, giving a vesicular 
appearance to the organ; this is particularly evident in Cristatella. The in- 
ternal layer is a delicate transparent membrane, in which I could detect no 
trace of structure; it resists putrefaction longer than the external cellular 
layer, and forms the immediate walls of the tubular cavity. A nervous fila- 
ment and muscular fibres, to be presently described, may also be traced into 
* Recherches sur l’Organisation des Laguncula, Nouveaux Mémoires de l’Acad. Roy. de 
Bruxelles, yol. xviii. 
