The American Eepreseutatives of Distomum cygnoides. 415 



between the c?eca and the side-walls of tlie body. The so-called genital 

 glands lie in the middle third, while the greater part of the Uterus 

 lies in the lateral thirds. First beliind the ventral sucker are the 

 paired vitelline glands, connected with each other by the transverse 

 vitelline duct. There are frequently two follicles on one side and 

 three on the other, sometimes tree on both sides, but other vari- 

 ations occur, and occasionly one can only detect an irregulär mass 

 in place of one or both sets of follicles. The shell-gland is an in- 

 conspicuous organ situated between the posterior follicles of the 

 vitellaria. The Single ovary and the two festes are always con- 

 spicuous bodies regularly alternating from one side to the other of 

 the middle longitudinal line. The ovary may be right or left: in 

 18 preparations which I have to band 7 have the ovary on the left 

 and 11 on the right. It is a compact oblong organ which may vary 

 into oval, and in one case I have seen it about twice as long as 

 usual and somewhat beut upon itself. It lies about the same 

 distance behind the ventral sucker as this is behind the oral 

 sucker. The first testis is behind and on the opposite side from the 

 ovary, and the second testis is on the same side as the ovary. They 

 are long bodies with irregulär sides as if lobed but this may be 

 partly due to the shortening or other muscular contractions of the 

 animal. It seems probable that when the worm is extended to its 

 greatest length that the festes, and perhaps the ovary too, would 

 become long and rod-like. But, while this may be in a measure 

 true for every individual, it is not always the cause of one indivi- 

 dual possessing longer festes than another. In some cases the 

 anterior end of one body lies on a level with the posterior end of 

 the preceding one, but in other cases all three organs are separated 

 by an interval. In the animal figured the anterior testis measured 

 1 mm in length and the posterior one nearly 1'4 mm. In another 

 individual, especially lengthened and correspondingly narrowed, the 

 posterior testis measured nearly 2 mm. 



A characteristic of the uterus of tliis species seems to be its 

 arrangement in numerous folds along each side of the body, outside 

 of the intestinal caeca, and from the region of the vitellaria to the 

 bind end of the animal, while between the caeca there are comparatively 

 few folds. The uterus throughout its course has a very narrow 

 calibre, but the two or three folds of the terminal portion, lying 

 between the vitellaria and the ventral sucker, may be somewhat 

 broadly distended. Between the ventral sucker and the egenital 



