

DIGESTIVE SYSTEM. 129 



The removal of the integument from the visceral mass requires 

 care, hut presents no great difficulty. Special care is needed 

 at the posterior end of the mantle-cavity, where the parts are 

 rather firmly bound together. 



The dissection is greatly facilitated by frequent washing 

 under the tap. 



A. The Alimentary Canal. 



The alimentary canal is a convoluted tube, of nearly 

 uniform size along the greater part of its length, but pre- 

 senting special features in its anterior portion. 



1. The buccal mass or pharynx is the enlarged anterior end 



of the canal into which the mouth opens. It forms 

 a prominent rounded mass in the head, with stout 

 muscular walls, and will be more fully examined 

 at a later stage of the dissection (p. 134). It con- 

 tains the odontophore. 



Insert a seeker into the mouth, and note that it passes up- 

 wards into the buccal mass. 



2. The oesophagus is a narrow thin-walled tube, which 



arises from the dorsal surface of the buccal mass 

 and runs backwards, passing into the crop. 



3. The crop is a large fusiform thin-walled dilatation of 



the alimentary canal, lying partly in front of the 

 visceral hump, partly in the first turn of the spire. 

 It is widest about the middle of its length, and 

 gradually narrows behind. 



Fig. 32. Helix pomatia. Dissection from the right side to show the 



digestive and reproductive systems, (a. m. m.) 



A, anus. AG, albumen gland. B, buccal mass, c, sac of radula. Cd 

 cerebral ganglion. D, jaw. E, mouth. F, flagellum. G, genital aperture. 

 H, crop. HD, hermaphrodite duct. HG, hermaphrodite gland. I, intes- 

 tine. K, dart sac. L, mucous glands. LD, left bile-duct. |_L, left lobes of 

 liver. M, female portion of the common duct. N, male portion of the common 

 duct. O, receptaculum seminus. o', dilated end of receptaculum seminus. P, 

 penis, retracted. PG, pedal ganglion. R, rectum. RD, right bile-duct. 

 RL, right lobe of liver, s, ' stomach.' SD, salivary duct. SG, salivary gland. 

 T, tentacle. VD, vas deferens. NG, viscero-pleural ganglion. Y, eye. 2, 

 posterior end of foot. 



