OONTRIBTJTIONS TO AMERICAN HELMINTHOLOGY. 65 



The testis is a solid gland situated in the posterior third of the body. 

 The course of the vas deferens is shown in the figure. No internal 

 vas deferens was observed. The male outlet lies immediately behind 

 the bifurcation of the intestine, and is armed with sixteen alternately 

 large and small hooks, which differ considerably in form from those 

 of P. integerrimum. The free end of each piece is sharply curved ; 

 the attached end is shaped like a cross, the transverse piece of which 

 is longer on one side than the other. The longer pieces measure 0.02 

 mm., and the shorter ones 0.015 mm. "Whether there is any connec- 

 tion between the attached ends, I am unable to say. 



The comparative transparency of the body would render the examin- 

 ation of the internal organs of this species of Polystomum particularly 

 easy. I failed,»however, to satisfy myself as to their disposition, from 

 the cause noted above. 



As in P. integerrimum, there are two latei-al cushions, in this case 

 each situated in a depression, which communicate with canals (vaginse) 

 leading towards the middle of the body. The inner ends of these I 

 could not follow. A third canal, originating from an oval body with 

 brown contents (shell-gland ?), situated on the left side of the middle 

 line (ov, Fig. 9), likewise was observed to take the same direction. 

 The ovary (not represented in the figure) is situated in front of the 

 testis on the right side of the body. The short oviduct terminates 

 in a wide uterus, in which only a single egg can be accommodated at 

 one time. The egg-shell is somewhat thin, is destitute of the short 

 stump present in that of P. integerrimum, but has a rather large 

 operculum. 



In each of the two most active specimens of the worm which I 

 secured, a Gyrodactylus-like larva, similar to that of P. integerrimum, 

 and with eye-spots disposed in the same fashion, had already escaped 

 from the shell, and was moving actively within the uterine chamber.^ 

 The motions seemed to depend entirely on the muscles and the hooks 

 of the caudal disc. This had a rounded outline, except posteriorly, 

 where there was a square projection bearing the four posterior small 

 hooks. The disc measured 0.114 mm. across, and the twelve anterior 



23 According to Zeller (loc. cit., p. 269, note), " die Eier bei den jiingsten fortpflanzungsfahigen 

 Hamblasenpolystomen durclimachen ihre Entwickelung noch innerhalb des Eierleiters." I am 

 act sure wlietlier to conclude from this that, as in the present instance, larva and egg-shell are 

 extruded separately from the uterus. I am inclined to believe, however, taking into considera- 

 tion the size and advanced state of development of the larva, the absence of cilia, and the thin- 

 ness of the egg-shell, that this viviparous method is the normal in P. oblongum. 



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