NOTES ON LOPHOPUS CRYSTALLINUS. 
439 
is certainly employed for the purpose of locomotion, although, 
undoubtedly, as Dr. Allman observes, it is not capable of the 
active movements of Grystatella. 
The organization of L. Grystallinus, like that of the 
Polyzoa in general, is simple. It is provided with organs of 
digestion, circulation, respiration, and generation. The mus- 
cular and nervous systems also are well developed. 
The organs of digestion consist of a mouth, an oesophagus, a 
stomach, and intestine. The mouth is a simple, toothless orifice, 
round, or slightly crescent- shaped, placed in the centre of the 
lophopore or tentacular disc. Its margin is slightly raised, 
and continuous on the neural side, i. e. the part in which the 
nervous ganglion is situated, with a hollow valve-like organ 
of very peculiar formation, called the epistome , the true func- 
tion of which is doubtful. An oesophagus of considerable 
length connects the mouth with the stomach ; it usually de- 
creases in diameter until it approaches the cardiac orifice of 
the stomach, where it again expands. In some of the marine 
Polyzoa there is a distinct gizzard, but in Lophopus, as, pro- 
bably, in all the fresh- water genera, there is no such organ, 
the oesophagus opening directly into the stomach, which latter 
may be divided into two portions, the cardiac and pyloric 
cavities. The first consists of a cylindrical prolongation, into 
one extremity of which the oesophagus opens, while the other 
is continuous with the rest of the stomach, which terminates 
in a cul de sac. The pyloric cavity communicates with the 
intestine by a distinct orifice, which, from its peculiar con- 
struction, is capable of dilatation or contraction, and even of 
being completely closed. 
At the point of junction with the stomach the intestine is 
very wide ; it rapidly decreases in size, however, until, passing 
along the side of the cardiac cavity and the oesophagus, it 
terminates in a distinct anus, below the mouth at the concave 
side of the lophopore. 
We will next proceed to consider the organs of respiration 
and circulation. 
The lophopore supports a series of tentacula upon its 
upper margin. In Lophopus , and most other fresh- water 
genera, such as Cristatella, Plumatella , and Aicyonella , the 
neural margin of the lophopore is extended into two trian- 
gular arms, causing it to present the appearance of a deep 
crescent. This condition of the lophopore never exists in the 
marine species, where it is always orbicular. In all the genera 
it forms the roof of the perigastric space. 
The interior of these triangular arms is clothed with vibratile 
cilia, the tentacula are tubular, closed at their free extremity, 
and open by the opposite, through the lophopore into the 
perigastric space. 
