THE CIRRHUS AND ITS MUSCLES. 311 



course, for they proceed from the rouuded posterior end of the pouch, 

 and, converging anteriorly, attach themselves ultimately to the cuti- 

 cular wall of the seminal duct. In many cases this anterior part of 

 the seminal duct is also characterised by a thinner or tliicker fringe 

 of spines situated on the cuticle. Its course is also always straight 

 and extended, while that of the posterior part, situated at the base of 

 the cirrhus-pouch, is generally coiled or twisted. 



There can be no doubt as to the purpose of this muscular terminal 

 apparatus. It serves to protrude the penis, which in the state of rest 

 is more or less withdrawn, and lengthens it by the evagination of the 

 anterior end of the seminal duct. Under the pressure of the power- 

 fully contracting muscular pouch, the internal elastic mass reacts on 

 the free and pliant anterior end, until a regular prolapsus results, in 

 consequence of which the spinous fringe of the seminal ducts emerges, 

 and its windings adapt themselves more or less to the length of the 

 prolapsus. The retraction is accomplished by the above-described 

 longitudinal fibres, which pass through the interior mass, and are 

 physiologically antagonistic to the hollow peripheral muscle. 



The seminal duct, or vas deferens, proceeding from the rounded 

 posterior end of the cirrhus-pouch is destitute of special musculature. 

 Its walls consist of a thin and extensible glassy membrane, which is 

 a continuation of the above-mentioned firm cuticle, and lies loose in 

 the substance of the body-parenchyma. On the exterior there is 

 generally distinguishable a layer of clear, delicate nucleated cells, 

 which may be interpreted as a kind of epithelium, and which, so far 

 as one can judge from appearances, can hardly be referred to the con- 

 nective-tissue corpuscles. We shall consider this afterwards, when 

 describing the manner of development of the generative organs. 



In spite of the thinness of its walls, the seminal duct is in many 

 cases of considerable width — sometimes throughout its whole length, 



, a b f., 



Fig. 160. — Two proglottides of Tcenia setigera from the goose (after Feuereisen). 

 A, Male, and JB, Female development, a, end of the vagina ; 6, receptaculum 

 seminis ; c, yolk-gland ; d, ovary ; / and g, seminal vesicles ; h, testes, 

 (x about 40.) 



and sometimes only in a definite place — in the neighbourhood of the 



cirrhus-pouch. This is due to its contents, the spermatozoa, which 



accumulate in it in great numbers at the time of the male maturity, 

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