No. 3.] STUDY OF STENOSTOMA LEUCOPS O. SCHM. 273 



The second set (P.R.M.) I shall call pharyngeal retractor 

 muscle cells, on account of their function of retracting the 

 pharynx. 



The radial muscle cells are very numerous. Those from the 

 centre of the pharynx run to their attachment at the integu- 

 ment in a direction perpendicular to the long axis of the phar- 

 ynx. Those from the posterior end are inclined backward, while 

 those from the anterior end are inclined forward. These cells 

 vary much in length and width, — the longest ones being the 

 narrowest. They are from 25 /a to 50 /i in length and from 

 I /x to 5 /i in width. This difference in form is largely due to 

 their state of contraction. 



Both ends of these muscle cells are split up into numerous 

 fine thread-like processes which run between the muscle fibres 

 of the pharyngeal and body walls, and thus serve to attach the 

 cells. 



The muscle cells are finely granular and have very large 

 coarsely granular ovoid nuclei (Fig. 8, N.) located in the centre 

 of the cell. The largest of these nuclei are 5 /* in length and 

 3 /i in width. They have small round eccentrically placed 

 nucleoli (A'".') which are i /i in diameter. In the alum-carmine 

 sections from which Fig. 8 was taken the chromatin network of 

 the nuclei was seen. 



The pharyngeal retractor muscle cells (Fig. 8, P.R.M.) are not 

 as numerous as the radial muscle cells. They run from about 

 the middle of the pharynx backward, interweaving with the 

 radial cells, and connect with the body wall opposite the 

 anterior end of the intestine. These cells are like the radial 

 cells in structure. They are provided with coarsely granular 

 nuclei (Fig. 8, N.), but I could not make out that their ends were 

 broken up as is the case with the radial cells. 



At the opening between the pharynx and intestine the walls 

 of each are so arranged that they form a circular valve. This 

 valve (Fig. 8, V.) is formed by the turning in of the anterior 

 end of the wall of the intestine, to form a cup-like depression, 

 at the bottom of which the intestine is joined by the pharynx. 



This valve is lined with epithelial cells intermediate in charac- 

 ter between those of the pharynx and those of the intestine. 



Intestine. — The intestine is the posterior part of the alimen- 

 tary canal. It fills nearly the whole of the posterior, half of 



