42 ILLINOIS BIOLOGICAL MONOGRAPHS [322 



diameter anterior to the testis ; in ventral view it is circular, 0.094 mm. 

 in diameter. The oviduct passes posteriad and mediad, and the ootype 

 appears as a darkly stained area. The vaginae can be distinctly seen 

 and laterad of the ceca on either side there is a large cavity communi- 

 cating with the exterior. The uterus is empty; the folded walls of the 

 cavity are visible on the left side of the body. The vitellaria are strongly 

 developed. Masses of follicles occupy the dorsal and lateral regions of 

 the body but ventrally do not extend mediad of the ceca. Anteriorly 

 they extend to the region of the pharynx; there is a strand across the 

 body just behind the pharynx and in the intercecal area anterior to the 

 testis they are largely interrupted, permitting the structures in this 

 region to be made out. None of the vitelline ducts are visible. 



The excretory vesicles are anterior to and slightly laterad of the 

 ceca at the level of the caudal margin of the pharynx, but no ducts 

 could be seen. 



POLYSTOMA HASSALLI Goto 1899 

 [Figures 30 to 33] 



This species was described by Goto (1899) from the urinary blad- 

 der of Cinosternum pennsylvanicum from Maryland. The writer has 

 since collected the species from other hosts and localities. A single 

 specimen was found in the urinary bladder of Aromochelys carinatus 

 from Newton, Texas ; five were collected from the urinary bladder of 

 Aromochelys odoratus from Raleigh, North Carolina; two from the 

 urinary bladder of Cinosternum pennsylvanicum from Raleigh, N. C. ; 

 and three from the urinary bladder of Chelydra serpentina from Walker, 

 Iowa. 



The worms (Figs. 30, 31) vary from 1.3 to 2 mm. in length and 

 from 0.4 to 0.65 mm. in width. The caudal disc varies in shape from 

 hexagonal to cordiform and is of approximately the same width as the 

 body. The suckers are 0.12 to 0.16 mm. in diameter. The eighteen 

 hooks of the caudal disc have the usual arrangement and are described 

 by Goto. However, he reports the larval hooks as being 0.33 mm. in 

 length and the great hooks between the caudal suckers as 0.125 mm. in 

 length. This is evidently a typographical error, since he figured the 

 great hooks as about four times the size of the small ones. In the pres- 

 ent material the great hooks are the same length as stated by Goto and 

 the smaller ones are 0.033 mm. in length, which agrees with the figures 

 of Goto by a change of one place in the decimal point. 



The anterior sucker is ovoid, more pointed anteriorly. It may be 

 longer in either the anterior-posterior or lateral axis and varies in diame- 

 ter from 0.22 to 0.33 mm. The pharynx is spherical or oval and varies 



