POLYGYRA ALBOLABRIS AND LIMAX MAXIMUS 253 



lateral and posterior border of that gland, then, turning, it pro- 

 ceeds forward and downward on the outer part of the digestive 

 gland, approaching very closely to the first part of the intestine 

 at a short distance from the stomach; then, turning, it proceeds 

 upward and backward through the digestive gland to th.e border 

 of the pulmonary sac. In Its course through the digestive gland 

 it forms an exaggerated letter S (pi. 5, fig. 3; pi. 6, fig. 7, 8). 



The rectum continues along the border of the pulmonary sac 

 to the anus, which is situated near the respiratory orifice (pi. 5, 

 fig. 3, 8). On the outer side of the rectum, running its entire 

 length, is a band of muscular fibers, the function of which is, prob- 

 ably, to shorten the rectum and to assist in expelling its contents. 



The digestive gland (pi. 5, fig. 3, 9), was formerly regarded as 

 analogous to the liver of vertebrate animals, but the organ con- 

 tains a diastatic ferment, which converts starchy matters into 

 glucose, and is comparable to the pancreas in vertebrate animals. 

 It contains neither biliary pigments nor biliary acids. The liver 

 of vertebrate animals is not a digestive gland in the true sense of 

 the word, since neither the bile nor an infusion of the hepatic 

 tissues contains a digestive ferment. The name liver could not 

 therefore be appropriately applied to the digestive gland of the 

 Gasteropoda. 



The digestive gland is divided into two parts, the larger and 

 inferior of which occupies the outer part of the volution imme- 

 diately beyond the heart and renal organ. The smaller and 

 superior lobe, in conjunction with the ovotestis, occupies the 

 apical whorls beyond the stomach. 



In the digestive gland are innumerable ducts which unite 

 and form a large duct in each lobe of the gland, the three large 

 ducts uniting in one, which, in connection with the duct from the 

 superior lobe of the gland, enters the stomach at a short distance 

 from the beginning of the intestine. 



The digestive gland is composed of lobules, which are formed 

 by the enlarged commencements of tin* duels, and arc lined with 



