20 



only notable regional differences lie in the epithelium. 

 The coiuiective tissue is much the same throughout, and 

 is continuous with that of the body-wall in which the diges- 

 tive viscera are imbedded. The blood lacunae are very 

 numerous and communicate on the one hand with the 

 cardio-visceral, and on the other hand with the branchio- 

 visceral main blood vessels. 



The connective tissue is also penetrated by (a) the caeca 

 of the gonads, especially the spermatic tubules, and (b) 

 the delicate branched clear tubules of the enigmatical 

 refringent organ or pyloric gland (PI. IV., fig. 7). The 

 tubules of this organ are lined by low cubical cells, usually 

 non-ciliated, containing no concretions or granules, and 

 having no great resemblance to gland cells. They have 

 been called " chylific " and absorptive, but the function is 

 still undetermined. There are few, if any, muscle fibres 

 in the connective tissue of the alimentary canal until the 

 rectum is reached. 



The lining epithelium is for the most part ciliated, 

 especially in the oesophagus and intestine. The oeso- 

 phagus has slight longitudinal ridges and grooves, one 

 of which seems to continue the canal of the dorsal lamina 

 onwards to the stomach , while another is in relation with 

 the posterior fold coming from the lower end of the 

 endostyle. There are a few glandular (mucous) cells 

 scattered amongst the ciliated columnar cells of the 

 oesophageal wall. 



The stomach has projecting folds in its interior which 

 unite at its pyloric end to form the intestinal typhlosole, 

 and, in addition to some ciliated and mucous cells, it has 

 large masses of highly coloured markedly glandular cells 

 packed with yellow granules. The intestine, again, has 

 ciliated and gland cells, and in the rectum the gland 

 cells become fewer and die out. The termination of the 



