no PHYLUM MOLLUSCA 



agus, side by side ; the former passes between the two halves 

 of the pancreas and ends with the rectum ; the oesophagus goes 

 forward side by side with the anterior aorta to the middle of the 

 large liver and passes through it in company with the aorta. The 

 oesophagus is easily found by turning the stomach over. A small 

 ganglion with radiating nerves will be seen by the side of the 

 oesophagus near its junction with the stomach. 



The liver is an elongated body lying between the retractor 

 muscles of the head and of the siphon ; two ducts emerge from 

 it and pass through the pancreas to the stomach pouch. Loosen 

 and remove the connective tissue around the liver and raise it up ; 

 the oesophagus and the aorta will be seen to pass through it 

 toward the back of the animal and then forward to the head. 



Remove the siphon and split the wall of the head ; trace the 

 oesophagus to its forwara end. It will be seen to pass through 

 the ganglionic mass which constitutes the central nervous system, 

 and which is surrounded by a hard, cartilaginous capsule. In 

 front of this it meets and ends in the bulbous pharynx. Near the 

 forward end of the liver, and resting upon the oesophagus, will be 

 seen the median salivary gland, the duct of which may be traced 

 to the pharynx ; near the hinder end of the pharynx is a pair of 

 smaller salivary glands, which also communicate with it. Trace 

 their ducts to the end. The alimentary canal will thus be seen 

 to consist of the following organs : the muscular pharynx, with 

 which a pair of small salivary glands and a single, large salivary 

 gland communicate ; the narrow oesophagus ; the thick-walled 

 stomach ; the stomach pouch, which communicates with the stom- 

 ach by a valved opening ; the elongated liver, which communi- 

 cates with the stomach pouch by two long ducts ; the bilobed 

 pancreas ; the intestine, which leaves the stomach near the point 

 where the oesophagus enters it ; the rectum, which is joined by 

 the ink bag and passes to the anus. 



Exercise 4. Take the alimentary tract out of the body, pin it down, 

 and make a drawing of it ; label all its divisions. 



Slit open the stomach and examine its ridges. Slit open the 

 pharynx on the upper side ; note the large, chitinous jaws and the 



