315] NORTH AMERICAN POLYSTOMIDAE—STUNKARD 3S 



in a row at more or less regular intervals and their hooks all point 

 backward. 



The cuticular covering of the body is about 14/i in thickness, and 

 on the contraction of the body is thrown into minute folds and furrows. 



The anterior sucker is oval, 0.2 to 0.22 mm. in length and 0.23 mm. 

 in width. It opens into the pharynx (Fig. 18), a spherical structure 

 .0.3 mm. in width. There is a broad nerve commissure crossing the an- 

 terior part of the pharynx which contains large ganglion cells. From 

 this dorsal commissure a nerve passes ventrad on either side of the 

 pharynx. 



The digestive tract is of the simple triclad type, the pharj-nx is fol- 

 lowed by a short esophagus, 0.17 mm. in length in the sectioned worm, 

 and the diverticula extend as simple tubes almost to the posterior end 

 of the body. They are about 0.15 mm. in diameter and terminate blindly, 

 dorsal to the middle pair of suckers (Fig. 21). The ceca are lateral but 

 close together, separated by only 0.2 to 0.25 mm. They have the usual 

 fibro-membranous coat and epithelial lining, and were empty in the 

 sectioned individual. 



The testis is spherical or slightly longer than broad in well extended 

 specimens. It is slightly anterior to the middle of the body and is com- 

 posed of a large number of lobes or strands of cells, compacted and 

 enclosed in a membranous capsule. Cells with the chromatin of their 

 nuclei in all stages of division and mature spermatozoa were observed 

 in sections. The sperm duct arises at the anterior dorsal margin of the 

 testis and curves dorsad and eephalad. Anterior to the uterus it turns 

 ventrad and expands to form the seminal vesicle. From the seminal 

 vesicle a small ejaculatory duct leads through the cirrus sac and opens 

 into the common genital sinus. 



The ovary is ovoid or comma shaped, situated a short distance 

 anterior to the testis, and in aU three specimens is located on the left 

 side of the body ; but since in other species it may lie on either side, it 

 is probable that the examination of a larger number of individuals 

 would show specimens with the ovary on the right side. In dorsal view 

 it is from 0.16 to 0.2 mm. in length and 0.08 to 0.12 mm. in width, while 

 in the specimen that was sectioned it is 0.08 mm. in width and 0.3 mm. 

 in depth. The oviduct arises at the dorsal posterior margin and curves 

 posteriad, mediad, and ventrad where it opens into the ootype. The 

 vitello-vaginal canals open separately into the ootype, just ventral to the 

 origin of the genito-intestinal canal. The latter duct passes laterad, 

 then dorsad and anteriad, turns mediad almost to the median line of 

 the body, then dorsad and laterad, and opens into the intestine of the 

 side in which the ovary is located. The uterine duct passes to the right 



