57 



The Alimentary Canal. 



By far the greater portion of the alimentary canal lies 

 entirely within the proximal limb of the viscero-pedal 

 mass, and may be easily dissected in a specimen hardened 

 with formol by removino; the muscular body-wall of one 

 side, cutting through the attachment of the transverse 

 muscle bundles as close to the integument as possible. 

 The attachments of these to the opposite wall are then 

 cut through beneath the intestine and the bundles removed, 

 the digestive gland and the gonad are picked away, and 

 the stomach and intestine lie exposed to view. 



The mouth (^1/., fig. 3, PI. I.) is at first a wide slit 

 extending across the body between the anterior body-wall 

 and the anterior adductor. It is bounded dorsally and 

 ventrally by the prominent upper and lower lips, the outer 

 extremities of which are produced laterally to form the 

 dorsal and ventral labial palps respectively. The opening 

 soon contracts, so that the perforation in the muscular 

 body leading into the oesophagus is oval in form. The 

 latter {Al.c.l) is a short tube passing backwards and 

 slightly upwards towards the posterior and dorsal part of 

 the viscero-pedal mass, where it expands into the stomach 

 {Al.c.2), which forms a capacious sac, increasing in 

 diameter from before backwards. The stomach is sur- 

 rounded on all sides by the dark -green mass of the 

 digestive gland (D.g.). This is really paired, and forms a 

 thick lobe on each side. Each lateral lobe, however, 

 expands over the dorsal anterior and posterior sides of the 

 stomach, so that it seems to nearly envelope the latter. 

 If the digestive gland is carefully picked away prior to 

 laying bare the stomach, two ducts may be seen opening 

 into the latter. One is small, and opens on the posterior 

 and dorsal margin ; the other is much larger, and opens 

 into the stomach at its junction with the oesophagus ; it 



