EXPERIMENTS IN THE BREEDING OF CERIONS. 9 



species examined it is inserted on its right branch. The buccal retractor 

 (sometimes referred to as pharyngeal retractor) passes through the 

 nerve ring above both the pedal and pleural ganglia, as does the 

 esophagus, but it goes below the buccal commissure, whereas the 

 esophagus passes above it. This muscle spreads out fan-shaped at its 

 anterior end, where it is attached chiefly to the cartilaginous base of 

 the buccal mass. It divides into two distinct parts before reaching 

 the nerve ring or each branch may be further divided. In Cerion uva 

 there are 4 branches on the left and 2 on the right, while in Cerion 

 incanum and Cerion casdblancce no definite divisions are found. In 

 Cerion viaregis these divisions are very numerous and in Cerion cras- 

 silabris 3 occur on the left side and 2 on the right. 



The salivary ducts are very short and lead from a distinctly paired 

 gland. This gland covers the esophagus, to which it is firmly attached 

 for a distance of 6 mm. At the posterior end of the salivary gland the 

 esophagus is firmly attached to the buccal retractor muscle. The 

 same relationship holds good in practically all the species examined. 



The esophagus becomes perceptibly constricted as it follows the 

 several muscles backward into the visceral mass behind the salivary 

 glands. The anterior end of the stomach lies immediately behind the 

 pericardium and kidney. The walls of the stomach are remarkable for 

 their great length, narrowness, and thinness. The posterior end of the 

 stomach lies high up in the whorls of the visceral mass and it is at this 

 point that the two lobes of the liver discharge their secretion by dis- 

 tinct ducts. The posterior lobe of the liver occupies the upper whorls 

 of the shell, while the anterior lobe is distributed among the various 

 organs below this. Both lobes are brownish-gray in color. The 

 intestine forms a tube slightly larger than the esophagus and passes 

 forward from the posterior end of the stomach. It makes the charac- 

 teristic visceral loop back of the pulmonary cavity. In some of the 

 species it is embedded in the albumen gland of the genital system, but 

 in Cerion crassilabris and Cerion viaregis the albumen gland is free and 

 the visceral lobe is rather imperfect. The intestine passes forward 

 on the right side of the pulmonary cavity, to the dorsal wall of which 

 it is firmly attached. In this region it is slightly larger than on the rest 

 of its course and in Cerion incanum and Cerion crassilabris it appears 

 to contain some glandular tissues in this region. The entire length of 

 the alimentary tract amounts to about 85 mm. in Cerion incanum. 



The pulmonary cavity occupies more than one whorl of the shell 

 when the animal is expanded. Its dorsal wall is thin, transparent, and 

 unmarked excepting a scarcely perceptible pigmentation along the 

 sides of the pulmonary vein. The pericardium and kidney are situated 

 at the posterior end of the pulmonary cavity. The former is shorter 

 than the kidney, but there is some variation in proportionate lengths. 

 The auricle discharges into the pulmonary vein which passes forward 



