250 



ZOOLOGY 



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 proglottis, where it 

 begins to branch, the ramifications 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 fertilise the ova. As 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," proglottides (Fig. 195), 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 meanwhile having 

 become absorbed. "3£» 



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 con- 

 tained within the eggs have meantime assumed 

 the form of rounded bodies, each armed with 

 six chitinoid hooks — the six-hooked or hexacanth 

 embryo (Fig. 196, A) enclosed within two membranes. If the pro- 

 glottides, or the eggs which have escaped from them, should now 

 be taken into the alimentary canal of the Pig, which forms the 

 ordinary second host of the parasite, the hooked embryos, becoming 

 freed from their coverings, bore their way with the aid of their 

 hooks through the wall of the alimentary canal, and reach the 

 voluntary muscles. Here they increase greatly in size, and develop 

 into rounded cysts with a large cavity filled with watery fluid — the 

 proscolex stage (B). On the wall of the proscolex, at one side, is 

 formed a hollow ingrowth, or invagination (C) ; and on the inner 

 surface of this are developed the hooks and suckers characteristic 

 of the head or scolex of the adult (D). When these are fully formed 

 the hollow ingrowth becomes everted (E), the suckers and hooks thus 

 coming to be situated on the outer surface (F). The whole embryo 

 has now the form of a bladder or vesicle, with which is connected 

 at one point a process having all the characters of the head and 

 neck of the mature Taenia solium ; this is the bladder- worm stage, 



pro- 



FlG. 105.- 



glottis of Taenia 

 solium. (After 

 Leuckart.) 



