810 REPORT—1850. 
From the mouth an esophagus of considerable length leads downwards to 
the stomach ; it becomes gradually narrower as it approaches the latter, into 
which it opens by a very distinct conical projection. 
To the esophagus immediately succeeds the stomach, without the interven- 
tion of any distinct gizzard, such as we find in Bowerbankia and certain 
other marine Polyzoa; and I cannot explain the statement of so excellent an 
authority as Siebold, who asserts that he has seen in Aleyonella a gizzard 
with an organization precisely similar to that of Bowerbankia*. The stomach 
is a large thick-walled sac, and may be divided into two portions, first a 
nearly cylindrical prolongation, which by one extremity immediately receives 
the cesophagus, while by the other it is continuous with the remaining por- 
tion of the stomach; it may be called the cardiac cavity of the stomach. 
The second division forms the greater portion of the stomach ; it is also of a 
nearly cylindrical form; its direction is almost continuous with that of the 
former, but it is longer and wider; it terminates below in a rounded cul-de- 
sae; to distinguish it from the other, I shall call it the pyloric cavity of the 
stomach. Between the cardiac and pyloric cavities there is no marked line 
of demarcation, the structure of both being quite similar; notwithstanding, 
however, the similarity of structure, I believe there are physiological grounds 
for the distinction, for I consider the cardiac cavity as the true homologue of 
the gizzard in Bowerbankia. 
On a level with the continuation of the cardiac into the pyloric cavity 
arises the inéestine; it springs from the pyloric cavity, with which it com- 
municates by a very defined orifice. The pylorus is distinctly valvular, and 
is furnished with prominent lips, which project into the intestine, and admit 
of the orifice being dilated or contracted, or even completely closed. The 
intestine is very wide at its origin, and passes up along the side of the cardiac 
cavity and cesophagus, rapidly diminishing in diameter till it terminates in a 
distinct anus just below the mouth. 
Histology of Alimentary Canal.—The histological structure of the alimen- 
tary tube is somewhat complex. In the walls of the stomach I have suc- 
ceeded in detecting three distinct layers. InternaHy we have a thick layer of 
a yellowish: brown colour ; this is thrown into strong longitudinal rugz, which, 
however, become less prominent in the czl-de-sac of the pyloric cavity; 
it is composed of transparent spherical cells filied with a clear fluid con- 
taining brown corpuscles. When the animal has been long left without food 
the brown corpuscles disappear from the cellules, and the stomach becomes 
colourless. Externally to this coloured layer, which we may perhaps view 
as the representative of the liver, is a layer of elongated colourless ecellules, 
whose long axes are placed perpendicularly to the surface of the stomach. 
The third and most external layer consists of delicate circular fibres which 
surround the stomach, and are without doubt muscular; these fibres are 
particularly evident towards the fundus of the pyloric cavity, and are much 
less distinct as we ascend towards the cesophagus. The fundus of the pyloric 
cavity seems indeed to differ from the rest of the stomach in structure and 
function ; the strong longitudinal rugee and deep brown colour of the internal 
layer nearly disappear in it, and during the process of digestion we may per- 
ceive that the peculiar peristaltic action of the walls is more marked in it than 
in the remainder of the cavity, from which it is every now and then separated - 
by a momentary hour-glass constriction. 
In the cesophagus the internal layer of brown-coloured cellules is wanting, 
and thereare no longitudinalruge. The layerof elongated cellules, however, 1s 
well-developed, and gives to this part of the alimentary canal a sort of tesselated 
* Lehrbuch der Vergleichenden Anatomie der Wirbellosen Thiere, § 38. note 1, 
