SEA-FISHERIES LABORATORY. 211 



absorptive surface of the intestine). Many investigations 

 have been made on their power of secreting enzymes, and 

 the results obtained are confusing. Macallum* investi- 

 gated the structures in Acijjenser, taking particular care 

 to avoid the entrance of enzymes from the alimentary 

 canal and pancreas, and found no certain evidence of a 

 digestive action of their secretion on starch or proteid. 

 Bonduoyf obtained the opposite results, finding the secre- 

 tion of the caeca in many Teleosts to behave like trypsin 

 and to act strongly on starch and proteid. Macallum sup- 

 poses that they represent the remains of a former series 

 of digestive diverticula of the alimentary canal. These 

 became restricted in most vertebrata to certain regions 

 forming the digestive glands of the canal, but a variable 

 number, however, persisted in Teleostomi as the pyloric 

 caeca. 



The remaining portion of the intestine lies on the 

 ocular side of the body cavity. The duodenum passes 

 into a tract of intestine which lies along the ventral and 

 anterior walls of the body cavity to the left of the rectum. 

 This is thrown into two S-shaped loops which terminate in 

 the rectum. Near the anus the muscle layer becomes 

 thicker, and the terminal portion of the rectum is also 

 connected to the adjacent body wall by strands of connec- 

 tive tissue. 



The Mesenteries are difficult to study on account of 

 the convolutions of the intestine. They are best examined 

 in a specimen, well hardened with spirit. Two mesen- 

 teric sheets appear to .be present, though these may pos- 

 sibly represent a single structure. One takes origin from 

 the dorsal and posterior walls of the body cavity in the 



* Jour. Anat, cind Phys., vol. xx., pp. 604-636, 1886. 

 f Arch. Zool. Exper., vii., pp. 419-460, 1899. 



