238 MORPHOLOGY OF INVERTEBRATE TYPES 



ward, perforates the liver, emerges on the lower surface of the 

 latter between the two hepatic ducts and opens into the stomach 

 near the middle of the visceral mass. The liver is embryologic- 

 ally a paired gland, but the two glands grow together during 

 development, and in the adult squid the liver resembles a long 

 cone with its base toward the head and its somewhat drawn- 

 out apex toward the rear. The right and left hepatic ducts enter 

 the nephridial sac, pass through the U-shaped pancreas and after 

 receiving the numerous minute ducts of the latter emerge as 

 hepato-pancreatic ducts. These soon unite and open as a com- 

 mon hepato-pancreatic duct into the stomach-pouch. The 

 stomach has thick muscular walls and communicates directly 

 with the stomach-pouch (called also ccecum or spiral stomach) 

 which is a long sac with thin muscular walls. When fully ex- 

 tended the stomach pouch reaches the rear end of the body. 

 Close to the cardiac opening of the stomach connecting it with 

 the oesophagus, is the pyloric opening leading from the stom- 

 ach into the intestine. The cardiac and pyloric openings are 

 controlled by sphincters. The opening between the stomach 

 and the stomach-pouch is controlled by the gastric valve, that 

 between the pouch and the intestine by the intestinal valve, and 

 the one between the common hepato-pancreatic duct and the 

 pouch by the hepatic valve. The intestine is a short tube running 

 forward and downward between the two lobes of the pancreas. 

 The intestine soon becomes constricted and leads into the 

 rectum which is about half as long as the liver. The rectum ends 

 at the base of the funnel in an anal chamber the entrance to 

 which may be closed by the anal sphincter. The anus is pro- 

 vided with an upper and lower lip and two lateral leaf-like pro- 

 cesses rectal papilla. 



Embryologically and histologically the alimentary canal may 

 be divided into three parts. The foregut or stomadeum includes 

 the bulb, oesophagus and stomach, and is lined with a chitinous 

 cuticle. The midgut includes the stomach-pouch and the in- 

 testine and is lined with ciliated epithelium rich in unicellular 



