305] NORTH AMERICAN POLYSTOMIDAE—STUNKARD 25 



The pharynx is approximately spherical, altho various states of con- 

 traction influence its shape to some extent. It does not lie directly in the 

 long axis of the body but obliquely, tlie lumen extending from the some- 

 what ventral anterior opening from the oral sucker to a more dorsal pos- 

 terior opening into the esophagus or intestine. In certain species it is 

 composed of two portions, (Figs. 6, 33) tho both are enclosed in the same 

 external capsule. In the anterior portion there are many strong annular 

 fibers and this part probably acts as a spliineter. altho there are also 

 radial fibers which extend from the external limiting membrane to the 

 cuticula of the lumen. In the posterior part the annular fibers are con- 

 fined almost entirely to the external region and a small central zone 

 (Fig. 25). The muscle fibers are branched and non-nucleated. Scattered 

 among the fibers in the posterior part there are large nuclei, each with a 

 deeply staining nucleolus and surrounded by a granular or flaky area 

 that is continued by a fine duct traceable by the presence of the same 

 granular substance and leading to the lumen of the pharynx. Goto 

 described somewhat similar nuclei in the pharynx of Diclidophora and 

 regards them as remnants of the cells that have produced the muscle 

 fibers. The writer is inclined to the view that in Polystoraa the granular 

 substance is a secretion. No extra-esophageal glands were observed, but 

 that the secretion of the pharyngeal cells is salivary was not demon- 

 strated. 



A short esophagus may be present in certain species (Fig. 6) but in 

 most cases the pharynx appears to open directly into the intestine at the 

 juncture of the right and left ceca. There may be a short median or 

 paired lateral pockets of the intestine extending anteriad from the junc- 

 tion of the ceca. 



There is wide variation in the type of the intestinal diverticula. In 

 P. iniegcrrimum the ceca are much branched and the.se branches ramify 

 thru the body and the caudal disc (Fig. 45). In P. alluaudi the ceca oc- 

 cupy the same location but are merely lobed and have no secondary 

 branches, tho they are united posteriorly. In P. buUiense, according to 

 Johnston, "a diverticulum from the buccal cavity i-iuis backwards, ven- 

 tral to the pharynx, and for a distance equal to its length forming a me- 

 dian unpaired buccal pocket." In all other known species there is a 

 simple bifurcate intestine, the ceca terminating just anterior to the caudal 

 disc. In two specimens of P. hassalli, however, the ceca are connected 

 posteriorly; in one of them tlie ends of the ceca are continuous and in 

 the other there is a connection some distance anterior to the ends of tlie 

 ceca (Fig. 30). The walls of the diverticula are composed of a delicate 

 fibro-membranous tissue upon M-hich rests the digestive epithelium. Tlie 

 einthelial layer consists of columnar cells whose nuclei lie near the fibro- 



