144 MOLLUSCA. 



1. The buccal mass. This is a rounded, muscular organ, 

 with a double ring of tissue, the buccal membranes, at its anterior 

 end, that surrounds the horny jaws. Examine the jaws and see 

 which is the larger. 



2. Behind the buccal mass are the paired salivary glands. 



3. Trace the narrow esophagus from the posterior end of the 

 buccal mass backward. At the base of the head it enters the 

 liver, a large, white organ that lies between the retractor muscles 

 of the head, and extends from the base of the head to a point dor- 

 sal to the external openings of the kidneys. Lying close to the 

 esophagus and covered by the anterior end of the liver is an elon- 

 gated median salivary gland, the duct from which follows the 

 esophagus into the head. The esophagus leaves the liver about 

 midway of its length, and follows along the ventral surface nearly 

 to the stomach. Before Entering the stomach the esophagus 

 passes the pancreas, a white, lobed organ that Hes just beneath 

 the glandular portion of the kidneys, and the systemic heart, a 

 roughly diamond-shaped organ that lies between the branchial 

 hearts. 



The stomach proper is a rather small, thick-walled sac that 

 lies on the right side of the body, dorsal and posterior to the right 

 branchial heart. From the left side of the stomach a rather 

 large opening leads into a thin-walled blind sac, the visceral sac, 

 that when filled with partly digested food, as it frequently is, 

 extends posteriorly to the end of the body and occupies a consid- 

 erable part of the conical portion of the body. When empty, 

 it is quite small and inconspicuous. 



The intestine leaves the stomach very near the point the eso- 

 phagus enters, and just anterior to the opening that leads into 

 the visceral sac. It passes ventrally, and becomes visible from 

 the surface, where its position has already been noted. 



Draw a figure showing the digestive system. 



Cut a median sagittal section of the buccal mass, and notice 

 the mouth cavity, the jaws, the muscles that move the jaws, the 

 tongue, and the position of the radula. Is the radula arranged 

 in the strap-over-pulley manner that it is in Busyconf 



