128 MOLLUSCA. 



organ that lies between the retractor muscles of the head, and 

 extends from the base of the head to a point dorsal to the exter- 

 nal openings of the kidneys. Lying close to the esophagus and 

 covered by the anterior end of the liver is an elongated median 

 livary 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 stom- 

 ach. Before entering the stomach the esophagus passes the 

 pancreas , a white, lobed organ that lies 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 Sycotypus f 



Draw a figure of the section. 



Male Reproductive System. The position of the penis has 

 already been noticed. Cut the tissue away from the base of the 

 penis and notice the swollen spermatophoric sac in which the 

 spermatophores are formed. Through the walls of the base of 

 the penis and the spermatophoric sac, groups of slender, light- 

 colored spermatophores can be seen. They will be studied later. 

 The vas deferens consists of three distinct parts: 



