PHYLUM PLATYHELMINTHES 235 



I surface, and extending throughout the greater part of the length 

 : and breadth of the proglottis. With each lobe is connected a fine 

 efferent duct ; the ducts of neighbouring lobes unite together to 

 form somewhat larger ducts ; and the larger ducts, receiving 

 numerous tributaries, eventually open into the inner extremity of 

 the vas deferens, or main duct of the testis. The vas deferens is a 

 convoluted tube which extends outwards towards the lateral 

 margin (right or left as the case may be) of the proglottis. 



The terminal part of the vas deferens, which is somewhat nar- 

 rower than the rest, traverses a narrow protrusible process, the 

 cirrus or penis, and opens at its extremity by the male genital 

 aperture. The cirrus is enclosed at the base by a muscular sac, the 

 cirrus ac^ 



The ovary (or.) differs from that of the Liver-Fluke in being a 

 paired organ, consisting of two approximately equal, right and 

 left, halves. It is situated towards the posterior border of the pro- 

 glottis. Like that of the Liver-Fluke, it consists of a number of 

 branching tubes, in the interior of which the ova are developed. 

 From opposite sides these tubes converge towards the median 

 line, where they open into the oviduct. A yolk-gland (gl. vit.), of less 

 relative extent than in the Liver-Fluke, consists of a number of 

 minute lobules ; a duct, the yolk-duct, which runs forward from it, 

 opens into the oviduct. The numerous lobules of a rounded shell- 

 gland (schld.) surround the yolk-duct where it passes forward to 

 join the oviduct ; and the uterus (liter.) opens into it at this point. 

 A short distance from its origin the oviduct -presents a dilatation, 

 the reccpt(.:tflttj)i seminis, in which the secretion of the testes is 

 stored during copulation. The remainder of the oviduct, frequently 

 known as the vagina (vag.), is a long narrow tube leading to the 

 female generative opening. The uterus is, in the segments in which 

 it first makes its appearance, a simple cylindrical diverticulum 

 of the oviduct ; it retains its simple form as far back as about the 

 600th proglo^JL where it begins to branch, the ramifications 

 increasing jfl ^M 1 and volume in the posterior segments. 



The test^BnHlecretion (probably from the same proglottis) 

 passes in theri^of copulation along the vagina to the rcceptacu- 

 lum seminis. Here, or in the proximal part of the oviduct, it 

 fertilises the ova as they ripen and become discharged from the 

 ovary. As in the case of the Liver-Fluke, the oosperm proper be- 

 comes surrounded by a quantity of food-yolk developed in the 

 yolk-glands, and is then enclosed in a firm chitinous shell formed 

 for it by the secretion of the shell-gland. It then passes into the 

 uterus. The first completed eggs are found in the uterus in some 

 proglottis between the 400th and the 500th. From this point 'back- 

 wards they rapidly accumulate, until the cavity of the uterus, 

 which now . becomes branched, is filled and distended with them. 

 Eventually in the most posterior, so-called " ripe " proglottides 



