NEW MAMMALIAN TAPEWORMS. 999 



point of agreement, in the similarity of the enclosure of the eggs 

 in numerous paruterine organs, which perhaps outweighs the 

 various dissimilarities which will be dealt with in considering the 

 testes and the ovaries and their ducts. The testes occupy in 

 Thysanotcenia lemuris a quite different position in the body from 

 that which they occupy in Th. gamhiana. They lie in the former 

 species entirely between the water-vascular tubes, and in the 

 medullary region of course of each proglottid. Lil^e the other 

 organs of the genital system, they commence to be visible rather 

 late in the body, thus contrasting very markedly with the 

 conditions obtaining in the second genus described in the present 

 paper. The testes lie mainly in the posterior region of each 

 proglottid, but in front of the transverse water-vascular vessel. 

 They form continuous rows each only one deep, and not, except 

 perhaps here and there, at all crowded. The testes are also 

 extended anteriorly to quite the fi-ont end of the proglottid on 

 either side of the ovaries. 



The cirrus sac is divided, but not sharply, into two regions. 

 The terminal part which encloses the cirrus is narrow, and this 

 tnbe expands posterioi'ly into an oval vesicle of much greater 

 dimensions. The whole structure has in fact much the shape of a 

 soda-water bottle. The hinder part of the sac is about on a level 

 with the receptaculum seminis and the sac itself is gorged with 

 sperm, the whole of the available space being filled with a mass of 

 spei'ni. It is encircled by a thick layer of nuiscle fibres which 

 i-un longitudinally to the longer axis of the sac, and form a 

 continuous coat passing in this direction to all round the sac 

 when it is viewed in longitudinal section, that is in transvei'se 

 sections of the proglottid. At the posterior end the thick 

 muscular layer is interrupted for a minute space, to permit of 

 the entrance of the sperm-duct which narrows greatly at its 

 entrance into the cirrus sac, or rather into that part of the 

 cirrus sac which is specialised as a vesicula seminalis. This 

 narrow region of the vas deferens immediately widens out 

 into a long tract of duct, which may be regarded as a second 

 vesicula seminalis. This tube is wide, cjuite as wide as in species 

 of Bertiella, and is coiled upon itself as it passes back towards 

 the opposite extremity of the body. This region of the sperm- 

 duct would be, if unwrapped from its coiling, of considerable 

 length ; I found it to be gorged with sperm. The cirrus itself 

 was generally protruding from the genital aperture. It is not 

 large and has the usual structure of this organ. The difference 

 which it shows from the sperm-duct is very striking, and 

 furnishes an argument in favour of those who would hold that 

 the cirrus is not merely the end of the sperm-duct which is 

 capable of proti-usion. It seems in this species at any rate to be 

 a structure independent of the sperm-duct. There is a certain 

 resemblance between the bottle-shaped cirrus sac and the bottle- 

 shaped receptaculum seminis and the end of the vagina. Both 

 of these tubes lie to the same side of the lateral excretory vessels — 



68* 



