200 ZOOLOGY 
and its sac attain an extraordinary length in the limpet, often 
twice the length of the animal; they lie between the viscera 
and the muscular foot. Two pairs of yellowish salivary glands 
pour their secretion into the buccal cavity by two ducts on 
each side, and many mucous glands also open into it. 
The oesophagus leads from the buccal mass into the stomach. 
The walls of this organ are much folded, it receives by 
numerous ducts the secretion of the liver. The latter is a 
large organ occupying the greater portion of the space in the 
visceral hump, and enveloping a considerable proportion of the 
Fig. 121.—Semi-diagrammatic view of 
intestinal coils of Patella vulgata. After 
R. J. Harvey Gibson. 
1. Buccal mass. 
. Rectum. 
Crop. 
. Stomach, 
oO FP cw ND 
. Coils of intestine. 
alimentary tract. The intestine which passes from the true 
stomach makes a loop and then again enlarges into a second 
stomach, which is bent upon itself; after this the intestine coils 
in a most complicated way and ultimately ends in a rectum, 
which opens to the exterior on the anal papilla in the anterior 
pallial chamber (Fig. 119). The whole alimentary canal is lined 
throughout by ciliated cells; the extent of its convolutions are 
shown by the fact that it may attain a length of over fourteen 
inches, in an animal a little more than an inch long. 
The heart consists of a single auricle and ventricle, in 
the allied forms Haliotis and Fisswrella two auricles exist. It 
is enclosed in a pericardium situated in the posterior angle of 
the anterior pallial chamber. A large vessel, the branchial 
vein, runs on each side round the edge of the mantle at the base 
of the gills; anteriorly the two vessels unite and empty into the 
auricle. A muscular valve separates the auricle from the ven- 
tricle. The cavity of the latter is much broken up by strands 
