323] NORTH AMERICAN POLYSTOMIDAE— STUNK ARD 43 



in width from 0.1 to 0.14 mm. ; it may be longer in either axis. There 

 is no esophagus, but in some specimens a median pocket of the intestine 

 extends anteriad from the bifurcation to the pharynx. In others, and 

 this is a more usual condition, lateral pockets of the intestine extend 

 anteriad, one on either side of the pharynx (Fig. 33). The anterior 

 sucker and pharynx are lined with cuticula; the intestine with the 

 usual digestive epithelium. In those specimens in which the uterus 

 contains an egg, the large size of the egg causes the ceca to be widely 

 separated at the uterine level and they approach each other behind the 

 uterus. In one specimen, median branches from the two ceca fuse and 

 form a posterior connection of the diverticula (Fig. 30), and in another 

 the two ceca are united at their ends. 



The testis is situated ventrally, just behind the middle of the body. 

 It is a somewhat shapeless mass, roughly oval in outline, crosswise of 

 the body, extending between the ceca just posterior to the uterus. The 

 vas deferens passes anteriad, dorsal to the ovary and between it 

 and the uterus; anterior to the uterus the sperm duct turns ventrad, 

 enlarges to form a seminal receptacle, and then passes thru the cirrus 

 sac, opening into the genital atrium (Fig. 32). The cirrus hooks are 

 sixteen in number, 0.028 mm. in length, straight, and with a wing like 

 process at the middle as described by Goto. 



The ovary is comma shaped or ovoid in outline, situated obliquely 

 in the body, on either the right or left side. Typically the ovary is on 

 one side of the body and the uterus on the other, but the enormous size 

 of the egg causes the uterus to occupy a more or less central position, 

 crowding the ovary far to one side. The ovary is 0.058 by 0.065 mm. 

 in the smallest and 0.085 by 0.12 mm. in the largest worms, altho the 

 size of the ovary does not correspond precisely with the size of the 

 worm. The oviduct arises at the dorsal median and posterior part of 

 the ovary and after a dorsal loop it turns posteriad and ventrad to open 

 into the ootype. Mehlis' gland is present. The genito-intestinal canal 

 branches from the ootype and after a short winding course opens into 

 the intestine near the ovary. From the ootype, the uterine duct passes 

 laterally to the opposite side of the median line and then anteriorly 

 and dorsally to open into the dorsal posterior part of the uterus. The 

 vitellaria extend from the pharyngeal region to the anterior margin 

 of the caudal disc; there is a row of follicles across the dorsal surface 

 behind the pharynx but they are absent between the ceca anterior to 

 the testis. According to Goto, "lobes not very numerous, separated 

 from one another, mostly confined to the lateral portion of the body, 

 but also present in the median portion behind the testis." The vaginae 

 are ventro-lateral, midway between the anterior and posterior ends of 

 the body. There are no vaginal prominences, the vaginal openings are 



