256 The Philippine Journal of Science ms 



of it as a pharynx. The upper part is held in position by means 

 of a mesentery radiating to the body wall. At the posterior 

 end, the dorsal surface is covered by the "heart," and the two 

 "connecting vessels" pass around it on opposite sides. The crop 

 is about 1 cm. long and from 2 to 3 mm. in diameter. It forms 

 a loop at the end of the oesophagus and turns to the left. It is 

 the thickest part of the canal, the thickness being due, not to 

 muscles, but to the large villus-like folds of the epithelium. The 

 remainder of the canal in front of the intestine is the midgut. 

 It passes posteriorly from the crop almost to the end of the body 

 and forms a U, turning again anteriorly. Here it widens into 

 the intestine. The midgut has a little larger diameter than the 

 crop, but the walls are very thin, and the folds of the epithelium 

 are much reduced. The beginning of the intestine is marked 

 by the opening of the collateral intestine, the siphonal groove 

 not extending beyond it. The intestine can as usual be divided 

 into 2 parts, the first part in this species being much shorter 

 than the second, which begins at the end of the collateral in- 

 testine and extends to the rectum. It bears a siphonal groove 

 all the way to the rectum. The first part is the widest region 

 of the alimentary canal, having a diameter of about 4 mm., while 

 the second part is considerably smaller. The walls of both are 

 very thin. The rectum is short, and into it on the left side 

 open the 2 anal trees. A small spherical diverticulum lies be- 

 tween them, and is attached by muscular filaments to the sheath 

 of the nerve cord. 



The oesophagus, crop, and intestine are held in place by means 

 of thick muscular filaments attached to their ventral surface. 

 The midgut is not attached to the body wall. A radiating mes- 

 entery connects the rectum to the posterior part of the body 

 wall. 



Microscopic structure. — The wall of the oesophagus (fig. 6) 

 is composed of three layers — ^the epithelium, the muscle and 

 connective-tissue layer, and the coelomic endothelium. The epi- 

 thelium consists of a layer of very long, slender, ciliated cells 

 with small nuclei at their bases. Lying between the ordinary 

 cells and opening on the surface are a great many long club- 

 shaped gland cells containing a granular material which is more 

 or less vacuolated. The submucous layer consists of a connective 

 tissue in which the muscle fibers are held. It varies in thickness 

 on account of the folding of the epithelium. The connective- 

 tissue cells are small with large nuclei and very long fibrous 

 outgrowths. In the inner part of this layer, muscle fibers of 



