gO COMPARATIVE ZOOLOGY. 



the intestines end in a large bladder-like expansion. Scor- 

 pions have no stomachal cavity a straight intestine passes 

 directly through the body. 



In bivalve Mollnsks, like the Clarn, the mouth opens 

 into a short oesophagus which leads into the stomach, 

 which lies imbedded in a large liver, and the intestine, 

 describing a few turns, passes directly through the heart. 40 

 In the univalve Mollusks, like the Snail, the gullet is long, 

 and frequently expands into a crop ; the stomach is often 

 double, the anterior being a gizzard provided with teeth 

 for mastication ; the intestine passes through the liver, 

 and ends in the fore-part of the body, usually on the right 

 side. 



The highest Mollusks, as the Cuttle-fish and Nautilus, 

 exhibit a marked advance. A mouth with powerful man- 

 dibles leads to a long gullet, which ends in a strong mus- 

 cular gizzard resembling that of a fowl. 41 Below this is a 

 cavity, which is either a stomach or duodenum ; it receives 



the secretion from 

 a large digestive 

 gland or pancreas. 

 The intestine is a 

 tube of uniform 

 size, which, after 

 one or two slight 

 curves, bends up, 

 and opens into the 

 "funnel" near the 

 mouth. 



Fishes have a 

 simple, short, and 

 wide alimentary 



PIG. 44. Alimentary Canal of the Oyster: a, stomach canal. The Stom- 

 laid open ; d, liver ; b, c, <?,/, convolutions of the intes- 

 tine; g, anal aperture; n, o, auricle and ventricle; /, acll IS Separated 

 w, adductor muscle; h, k, lobes of mouth divided to /. ,1 . , ,. 



show the venous canals at the base of the gills. 



