382 THE DOGFISH less. 



converts the intestine into a very long, closely-coiled tube, 

 and greatly increases the absorbent surface. Finally the 

 intestine opens into a large chamber, the cloaca {cl), which 

 communicates with the exterior by the vent. 



From the gullet backwards the enteric canal is contained 

 in the abdominal division of the ccelome, to the dorsal wall 

 of which it is suspended by a median mesentery (Fig. 99, 

 c, and Fig. 103, tnes). The greater part of the canal is de- 

 veloped from the enteron of the embryo, and is consequently 

 lined by endoderm ; only the oral cavity is formed from 

 the stoniodneum, and the cloaca from the proctodeum (Fig. 

 99, a). Outside the enteric epithelium are connective and 

 muscular layers, the latter formed of unstriped fibres : it is 

 generally characteristic of Vertebrates that the voluntary 

 muscles are striped, the involuntary unstriped. 



The digestive glands are characteristic. The largest is an 

 immense liver (Fig. 99, Lr) divided into two lobes (Fig. 

 103, /. /r, r. lr) and situated below the stomach along the 

 whole length of the abdomen, to the wall of which it is 

 attached by a fold of peritoneum. It discharges its secretion, 

 the bile^ into the commencement of the intestine by a tube, 

 the bile-duct (Fig. 99, B. D), which gives off a blind ofTshoot 

 terminating in a large sac, the gall-bladder (G. Bt) ; this 

 serves as a reservoir for the bile, the chief function of which 

 is to act upon the fatty portions of the food. But besides 

 secreting this special digestive juice, the liver-cells produce 

 a substance called glycogen or animal starch, which is passed 

 directly into the blood in the form of sugar. 



Another gland, of considerably smaller size, is the pan- 

 creas (Fig. 99, Pn Fig. 103, pan) \ it lies against the 

 anterior end of the intestine, into which it opens by the 

 pancreatic duct. It secretes pancreatic juice, which has an 

 action upon all the principal classes of food, converting 



