SEA-FISHERIES LABORATORY. 209 



appear to be present in tlie intestine of the plaice. Nor is 

 the peculiar " stratum compactum " of the submucosa 

 which Oppel has described in some other fishes certainly 

 present. 



The Stomach (fig. 21) is sharply distinguished from 

 oesophagus and duodenum by the strongly developed 

 transverse musculature at its proximal and distal ends. 

 The transverse muscle layer is less strongly and the longi- 

 tudinal layer more strongly developed than in the 

 oesophagus. At its pyloric end the transverse muscle 

 layer becomes much thicker and forms the prominent 

 sphincter pylori, a valve which projects into the cavity 

 of the duodenum. There is also a very marked differentia- 

 tion of the mucosa. In the oesophagus this consists of a 

 simple columnar epithelium with goblet cells. In the 

 stomach the goblet cells disappear and the epithelium is 

 evaginated to form a closely-set series of gastric glands 

 over the whole internal surface. Each gland is a tubule, 

 the internal portion of which is straight and the deeper 

 portion convoluted. The straight or conducting portion 

 has a wall consisting of columnar cells with a cement 

 substance between them, and the lumen is relatively wide. 

 The deeper or secreting portion has walls made up of large 

 cubical clear cells, whilst the lumen is narrow. The sub- 

 mucosa consists of loose areolar tissue containing blood 

 vessels. The stomach lies along the dorsal wall of the 

 body cavity, and the pylorus is situated at rhe posterior 

 end of the kidney. 



The Duodenum lies "along the posterior wall of the 

 body cavity towards the eyeless side of the body. Its 

 proximal end is slightly folded over the distal end of the 

 stomach. Its wall (and that of the succeeding regions of 

 the alimentary canal) is thin and consists of an outer longi- 

 tudinal and an inner transverse layer of unstriated muscle 



