325] NORTH AMERICAN POLYSTOMIDAE-STUN KARD 45 



as the " (shell gland?) "' is really the ovaiy. The lobes of the vitellaria 

 are scattered and extend from the pliarynx to the caudal lamina or disc. 

 It is doubtful whether Wright was correct in his statement that "The 

 transverse duct seemed to pass inward dorsally from the intestinal ceca," 

 since in all other known species the vitelline ducts are ventral in position. 



The uterus is described as containing a single large egg or embryo. 

 The egg shell is thin and is destitute of the short stump present in that 

 of P. integcrrimitm, but has a rather large operculum. In two cases the 

 embryo had already escaped from the shell and moved actively within 

 the uterine chamber. It is a Gyrodactylus-like larva, similar to that of 

 P. integerrimum, with eye spots disposed in the same fashion. It is 

 devoid of cilia, and movement seemed to depend entirely on the muscles 

 and hooks of the caudal disc. The latter had a rounded outline except 

 posteriorly where there was a square projection bearing the four small 

 posterior hooks. The disc measured 0.114 mm. across and the twelve 

 small anterior hooks were disposed at regular intervals on the margin of 

 the rounded part. There was no trace of suckers. The small hooks had 

 already attained their definitive size and form. The two large hooks 

 were situated considerably further in from the margin than in the adult, 

 and measured only 0.024 mm. instead of 0.15 mm. in length, which dif- 

 ference it is stated was due to the shortness of the immersed portion, in 

 which, however, the notch was already formed. 



In shape, as well as relative position and size of organs, P. oblangmn 

 strongly resembles P. hassalli. It is significant also that both are from 

 the urinary bladder of AromocheUjs odoratus. P. oblongum is slightly 

 longer and broader than P. hassalli, the posterior suckers are larger and 

 the small hooks of the disc are only about half the length of those in 

 those in P. lutssalli. The two species agree in number of genital hooks, 

 but in the former species the hooks are alternately large and small and 

 with the free end sharply curved, while in P. hassalli they are straight 

 and luiiform in size. 



The species in the genus Polystoma have been arranged in the form 

 of an analytical key utilizing the more prominent or more useful 

 diagnostic structures in separating the different forms. This key is 

 found on the following page. 



