692 DR. r. E. BEDDARD ON 



of those interstices. The cells are rather clear, with well-stained 

 nuclei. They correspond exactly, as it seems to me, with the 

 prostatic cells of Inermicapsifer and Zschokkeella, dealt with in 

 these genera by v. Janicki* and myself t, and which appear to 

 occur also elsewhere. In immature segments the cells bulk more 

 largely than the coils of the sperm-duct. But the reverse is the 

 case in the mature proglottid. 



The genital ducts open into a common cloaca genitalis, which in 

 its turn opens on to the exterior. The cloaca genitalis is of some 

 depth, but it is not borne upon any process of the body. Into it 

 open, close together, the vagina and the cii-rns sac, whose mutual 

 relations I have investigated by means of sagittal sections (text- 

 fig. 101) through portions of the strobila. There is a con- 

 siderable variation in these relations. Although the vaginal pore 

 is apparently never in front of the male poi-e, it is not always 

 directly behind the male pore. The commencing vagina lies 

 obliquely behind the commencing cirrus sac — the direction of the 

 obliquity being now dorsal now ventral in this segment and in that. 

 There is, in fact, an irregular alternation from segment to seg- 

 ment ; sometimes the two tubes are not merely oblique, but actually 

 dorsal or ventral to each other as the case may be, lying there- 

 fore side by side in sagittal sections. This recalls to mind the 

 alternation that occurs in certain (but not all) species of the 

 genus Moniezia, where the vagina may be dorsal or ventral to the 

 cirrus sac. But in this latter genus the alternation is of the 

 right and left set of generative organs of a single segment. 



The cirrtts sac of this tapeworm is large and has the very common 

 flask-shape. The neck-region has very thick circular muscular 

 walls, forming a sheath which thins out over the more distended 

 region of the sac. In less mature segments (in which, however, 

 the testes are fully developed, though with no mature sperma- 

 tozoa) the cirrus sac is elongated, gradually diminishing in breadth 

 towards the external pore ; there is no marked division into neck 

 and flask. It is very long and extends towards the middle line 

 of the body, a little beyond the water vascular tube of its side of 

 the body, or at least reaches the internal side of that tube. The 

 cirrus runs straight from end to end of the cirrus sac and 

 anteriorly presents a moniliform appearance, which is due to suc- 

 cessive dilatations of the lumen of the cirrus. This region of the 

 cirrus is both preceded and succeeded by a perfectly straight 

 section of that tube with very nari'ow lumen and thick walls. 



In later segments the cirrus sac acquires the flask-shape ah-eady 

 referred to. Coincidently with this is an actual shortening of the 

 length of the entire sac and a coiling of the cirrus within it. 

 The cirrus sac in these and in subsequent segments hardly reaches 

 beyond the outer edge of the water vascular tube. It seems clear 

 therefore that the shortening is due to an actual contraction of 



* Deiikschr. Ges. Jena, xvi. 1910. 

 t P. Z. S. 1912, p. 602. 



