680 DR. WILLIAM NICOLL ON 



groups of follicles, which extend from midway between the 

 intestinal bifurcation and the anteiior edge of the ventral sucker 

 to near the ends of the intestines. The initial part of the uterus 

 is practically empty. In section it can be made out with difficulty 

 as an extremely nari'ow tube, passing backwards from the shell- 

 gland. Behind the right testis it widens out to form a recep- 

 taculum seminis uterinum, consisting of about four or five small 

 dilatations. Further back a few ova appear, but the uterus 

 still remains somewhat narrow. When it has nearly reached the 

 posterior end of the body it turns abruptly on itself to form an 

 ascending limb. Almost immediately this begins to dilate, and 

 it has only proceeded a short distance before it almost completely 

 fills the interior of the body. It passes forward, over and between 

 the testes, crosses the venti'al sucker, and terminates in a straight, 

 thick-walled vagina, which is about half the length of the cirrus- 

 pouch, and lies on the left side. The utervis thus consists of 

 a descending and an ascending limb, the former being empty for 

 the greater part of its length, and the latter being enormously 

 dilated. The increase in size, therefore, takes place, not by an 

 increase in convolutions, but by a great dilatation of the ascending 

 limb. The ova are very numerous, rounded oblong in shape, and 

 dark brown in colour. They have a lai-ge well-marked operculum. 

 Many of them are more oval than oblong, and this gives rise to 

 some variation in dimensions. Fiom a large number of measure- 

 ments the limits were found to be •038-'045 mm. for the length, 

 and •018-'023 mm. for the breadth, and the average "040 X '021 

 mm. The extreme sizes observed wei'e '045 x "018 mm. for the 

 most oblong ova, and -038 x '023 mm. for the most oval. 



No case of amphitypy was observed in any of the two dozen 

 specimens forming the collection. The nearest approach was in 

 one specimen where the testes were practically symmetrical, the 

 left being a trifle behind the right, but the ovary and genital 

 aperture were normal. In all the other specimens the position 

 of these structures was exactly as I have described. The species, 

 however, is extremely variable in one respect, namely, the 

 posterior limit of the yolk-glands. Hardly two specimens agree 

 in this respect. In some specimens they extend a short distance 

 beyond the testes, in others they reach the middle of the posterior 

 testis, and again in others they stop shoi't of the testes. In 

 addition, they are very frequently asymmetrical, extending further 

 back on the rig^ht than on the left, or more rarely vice versa. The 

 fact, however, that their anterior limit is constantly symmetrical 

 induced me to consider a symmetrical posterior limit as the normal. 

 In two specimens also, the intestinal diverticula were of unequal 

 length, the left diverticulum being considei'ably shorter than the 

 right, which was normal. The position of the genital aperture 

 varied only very slightly, and most of the apparent variations 

 were due to contraction. The length of the cirrus-pouch was 

 practically constant, although in one specimen it extended nearly 

 to the posterior border of the ventral sucker. The size of the ova 

 was constant within the limits noted, and no increase in size takes 



