DIGESTIVE SYSTEM. 47 



stomach, as in Helix (snail), intestine, as in Lymnceus, rarely 

 in oesophagus, or partially externally, as in Doris. 



Pteropoda. Mouth furnished with sucker-bearing tenta- 

 cles. In other respects the canal closely resembles that of 

 Gasteropoda. Hepatic secretion from gastric follicles, as in 

 Clio. Salivary glands pour secretion into mouth. 



Cephalopoda. Mouth surrounded by prehensile sucker- 

 bearing tentacles, and a circular fold of skin which is serrated 

 at free edge. The parrot-like jaws encompass the opening 

 leading into a muscular pharynx, which is furnished with a 

 tongue upon its floor. Gullet, well defined, and extends 

 thence to a stomach, which is generally simple, and lined 

 with a mucous membrane thrown into longitudinal folds, 

 covered with horny epithelium. In Nautilus a crop precedes 

 the muscular stomach or gizzard. The intestine is narrow 

 and convoluted, and terminates in an anus within the mantle 

 upon the right side of body. Appended to the pyloric ex- 

 tremity of the stomach, in many Cephalopoda, is a globular 

 or spiral viscus, which secretes a fluid held to be analogous 

 to the pancreatic fluid of the Vertebrata. Salivary glands 

 well developed, generally two pairs, opening into gullet near 

 base of tongue by long excretory ducts. Hepatic secretion 

 from well-developed liver, which commonly surrounds the 

 oesophagus, the bile-duct opening into intestine at region of 

 pyloric appendage. 



ARTICULATA. As a rule, the alimentary canal begins upon 

 the dorsal aspect of the cranial segments and terminates 

 upon the ventral aspect of the terminal caudal segment. 



Rotifera. The mouth is simple and placed between the 

 ciliated disks. The armature of teeth (q. v.) succeeds to a 

 protrusile gullet emptying into a thick, simple stomach. 

 From this passes a narrow intestine, either curved upon it- 

 self, as in Melicerta, to terminate upon the side, or, more 

 straight, to open at caudal extremity, as in Rotifer. 



Two csecal appendages to stomach secrete a colorless fluid, 

 perhaps analogous to a pancreatic product. A hepatic secre- 

 tion is derived from gastric cells. 



Annelida. The mouth is usually surrounded with thick 



