246 ZOOLOGY SECT. 



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 many shell-gland ducts 

 open into the oviduct near its junction with the yolk-duct : this 

 part of the oviduct is the ootype the part in which the egg becomes 

 completed. In front this passes into the uterus. The female 

 genital pore, situated in the genital atrium, leads into a narrow 

 passage which runs inwards and backwards towards the middle 

 line of the proglottis, where it ends in a dilatation usually filled 

 with sperms the receptaculum seminis. From this a narrow duct 

 the fertilising duct or spermatic duct runs to join the oviduct. 

 The uterus, in the segments in which it first 

 makes its appearance, is a simple cylindrical 

 diverticulum of the oviduct ; it retains its 

 simple form as far back as about the -600th pro- 

 glottis, where it begins to branch, the ramifica- 

 tions increasing in extent and volume in the 

 posterior segments. It has no opening on the 

 exterior. 



Masses of sperms (probably from the same 

 proglottis) pass in the act of copulation along 

 the vagina to the receptaculum seminis ; through 

 the fertilising duct they pass to the oviduct to 

 ^ er ^ se ^ ne ova - && in the case of the Liver- 

 Fluke, the oosperm proper becomes 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 backwards 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," pro- 

 glottides (Fig. 198), the uterus, with its contained accumulation of 

 eggs, becomes so large as to fill the greater part of the interior of 

 the proglottis, the remainder of the reproductive apparatus mean- 

 while having become absorbed. 



Development. When the ripe proglottides are detached they 

 pass to the exterior with the faeces of the host. For a time they 

 exhibit movements of contraction. The embryos contained within 

 the eggs have meantime assumed the form of rounded bodies, each 

 armed with six chitinoid hooks the six-hooked or hexacanth embryo 



