39 



digi'stiuu ; that the tuud i^ cuiiiiuinutL'Ll and }iaitiaJl\' digested in tiie stomacli by 

 the digestive tkiids introduced from the caecum or from the pancreas and liver; 

 that the partially digested food then jjasses into the caecum for complete digestion 

 and absorption while the bones and indigestible residue are ejected from the 

 stomach through the intestine to the exterior. It is probable that the fluids from 

 the liver and pancreas pass into the caecum and from it to the stomach but it 

 is possible , as suggested above , that .these secretions may flow directly into the 

 intestine and thence to the stomach. 



The Livek and Pancreas. These glands arise from two long tubular evagina- 

 tions from the caecal portion of the mesenteron. These tubes extend outward to 

 the visceral wall and then forward as far as the skull. They are flattened 

 laterally between the yolk mass and the visceral wall. At first the wall of each 

 tube is formed by a plain cubical or palisadal epithelium but later each tube becomes 

 differentiated into three portions. The distal portion becomes a large racemose 

 gland which fuses with its mate to form a conical gland , the liver. The middle 

 portion of each forms a short hepatic duet. The proximal portion of the evagina- 

 tion forms one side of the pancreas. The two evaginations, originally independent, 

 are carried out by another evagination of the caecal wall , so that they 

 finally open together into the caecum. This secondary evagination becomes the 

 common hepatic duct and its walls becoming glandular , form the unpaired 

 portion of the pancreas. The fact that the liver and pancreas are originally paired 

 structures accounts for the passage of the oesophagus thru the liver and of the 

 intestine between the lobes of the pancreas. 



The liver is conical. Its broad ventral end rests upon the skull and its 

 pointed dorsal end lies beneath the middle of the pen. The ventral end of the 

 liver is in-egular because the median salivary gland is imbedded in it and because 

 the visceral and pallial nerves . and the oesophagus and aorta pass obliquel}' 

 through it in deep grooves or in canals. The groove for the oesophagus and 

 aorta continues backward to the middle of the upper surface of the liver. At 

 this point . it opens into a canal which passes obliquely downward and backward 

 to the lower side of the liver, ending between the hepatic ducts at a point about 

 one third the length of the liver from its dorsal end. The two hepatic ducts 

 emerge from the liver, one on each side of the oesophagus and aorta, and pass 

 immediately into a space between the siphonal retractors , and above the anterior 

 vena cava. After a short course in this space, they enter the pancreas which 

 lies in the nephridial cavity. The hepatic ducts and the liver are attached to sur- 

 rounding tissues by means of loose connective tissue. 



The liver is a compound tubulai- gland of light yellowish-brown color. The 



