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 



PiQ. 121. — Semi - diagraramatio view of 

 intestinal coils of Patella vulgata. After 

 R. J. Harvey Gibson. 



4...///./^^ /^ /,'C^^\\ 1- Buccal mass. 



2. Rectum. 



3. Crop'. 



4. Stomach. 



5. 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 Fissurella 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 



