392 DR. A. FARRE ON THE STRUCTURE OF THE CILIOBRACHIATE POLYPI. 
Fig. 2. The animal when fully expanded is about one twelfth of an inch in length. 
In its retracted state it is completely inclosed in a delicate horny cell, sufficiently 
transparent to admit of the whole structure of the contained animal being seen through 
its parietes. The cells are connected together by a cylindrical creeping stem, upon 
which they are thickly set, and sessile, ascending from its sides and upper surface. 
Fig. 3. a. The animal when completely expanded is seen to possess ten arms of 
about one third the length of the whole body, each arm being thickly ciliated on 
either side, and armed at the back by about a dozen fine hair-like processes, which 
project at nearly right angles from the tentacula, remaining motionless, while the 
cilia are in constant and active vibration. 
The tentacula are united together at their base to form a circle, in the centre of 
which is the mouth, and from which descends the oesophagus (fig. 3. a 1), bulging a 
little at its commencement, and then contracting and passing down nearly straight 
to its termination. The parietes of the oesophagus, especially at the upper part, which 
may be more correctly denominated the pharynx, are thickly studded with minute 
oval spots, arranged closely in contact with each other (Plate XXI. fig. 8.). The whole 
organ appears to be highly irritable, and contracts vigorously when food is introduced 
into it. 
At the termination of the oesophagus is a distinct cardiac orifice (fig. 3. a 2.) that 
opens into a small globular cavity (a 3.) of singular construction, which appears to 
perform the office of a gizzard. The parietes of this organ are thicker than in any 
other part of the alimentary canal. They contain two dark round bodies placed op- 
posite to each other, from each of which dark lines are seen radiating. In the space 
between these two dark bodies may be seen a number of squamiform spots arranged 
closely in contact, and presenting a beautifully regular tessellated appearance. This 
appearance was at first supposed to be owing to the crossing of the radiating lines at 
this point (fig. 4.) ; but a more accurate examination convinced me that they were 
distinct bodies lining a part of the interior of the cavity, and probably performing 
the office of gastric teeth : they have a remarkably definite outline when viewed under 
favourable circumstances, and by tearing open the gizzard, or bursting it by pressure, 
may be separated from its inner surface (Plate XXI. fig. 7 -)- The two dark bodies ap- 
pear to be the points at which the radiating lines are concentrated. When the organ 
is in a state of rest and viewed laterally, these are seen projecting into the cavity, and 
giving it an hour-glass form (fig. 5.) ; but when it contracts these bodies become 
elongated, and their inner surfaces are closely applied to each other, and the cavity 
is obliterated (fig. 6.). The alterations in the form of this organ appear to be entirely 
due to these apparently muscular bodies. They are conspicuous even in animals not 
yet arrived at maturity (fig. 3. c 1.). 
This organ, which I shall call the gizzard, opens downward into the true digestive 
stomach (fig. 3. a 4.), an oblong cavity terminating below in a blunt extremity, and 
from which it is separated only by the contraction of the parietes. The entire walls 
