THE FEMALE SEXUAL ORGANS. 



313 



As has been sufficiently shown by the foregoing remarks, the 

 differences in the male apparatus are of entirely subordinate import, 

 especially in so far as they are determined by the form and size of the 

 proglottides. But it is in this respect quite different with the female 

 parts, which, although also much affected in form and arrangement by 

 the above factors, exhibit, besides, other important characteristics. 

 These consist mainly in the structure of the yolk-gland, and are of so 

 fundamental a nature that we have to distinguish two types of it — 

 one which occurs in the Teeniadae, and another in the remaining tape- 

 worms (Bothriadse). As both have their representatives among the 

 human Cestodes, we shall now shortly consider them. 



One of these types represented in the Tseniadse is mainly char- 

 acterised by the absence of the uterine opening, and by the small 

 development of the yolk-gland, — characteristics which have a certain 

 connection with each other, since they both find their explanation in 

 the above-noted peculiarities of the breeding. The vagina, which, as 

 we have seen, is separate from the uterus, appears as a distinctly 

 marked narrow canal, which extends in a transverse direction from the 

 generally marginal porus genitalis (Fig. 162), and has either a straight 



Fig. 162. — Sexual organs of Tcenia perfoliata of the horse (after Kahane). 

 A, Joint in male maturity ; above, oirrhus, vas deferens with sessile testes ; 

 below, the yolk-glands, uterus with shell-gland and yolk-gland, vagina with 

 receptaculum. B, Female organs at the time of the transference of the 

 eggs into the ovarj'. (x 15.) 



course, or, as in the Tcenice with extended joints (Fig. 165), curves 



backwards towards the middle of tlie joint. Tlie posterior end enlarges 



into a receptaculum seminis of varying and sometimes considerable 



size, and is filled with semen at a time when tlie uterus contains 



as yet no eggs. The vagina itself is, on the contrary, generally empty, 



and its lumen is much contracted, obviously because the firm cuticle 



which covers it, especially in the posterior part, is very elastic, and 



quickly forces the introduced semen into the receptaculum. There is 



no muscular sheath in the vagina. The only layer found on the 



cuticle consists of a pretty thick epithelial layer, somewhat like 



that which we observed in the vas deferens. 



But the posterior end of the vagina not only leads into a sperm 

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