78 ILLINOIS BIOLOGICAL MONOGRAPHS [366 



skirts the uterus-sac. When it reaches the median line above the sack it turns 

 sharply downward and backward. The vagina has a diameter of from 15 to 

 20^1 opposite the middle of the cirrus-sac and is lined wdth only a comparatively 

 thin layer of cuticula. It very gradually expands after crossing the inner 

 end of the cirrus-sac to form a much elongated and very spacious receptaculum 

 seminis, the diameter of which close to its inner end may be as much as 90^. 

 This is usually filled in sections with spermatozoa, a stream of which may 

 often be seen passing on into the spermiduct. The beginning of the duct is 

 surrounded by a poorly developed layer of circular muscles which are almost 

 absent from the inner expanded portion. The receptaculum is sharply separa- 

 ted from the spermiduct which has a diameter of only 15 to 20ju and a length 

 of 0.12mm. The latter is an almost straight tube passing in the median line 

 from the more dorsally situated receptaculum to its point of union with the 

 oviduct close to the ventral wall of the medulla (Fig. 83). It shows best in 

 transections where its walls are seen to be composed of an epitheUum of cubical 

 cells lying on a distinct basement membrane, and to be surrounded with a 

 thick layer of nuclei and extremely few, if any, muscle fibres. The ovary 

 (Figs. 68, 83) is a somewhat kidney-shaped tubulolobular organ situated in the 

 posterior half of the proglottis behind the developing uterus-sac with its con- 

 cavity directed forward, and not exactly in the median fine but slightly ap-- 

 proaching the cloaca. It averages 0.45mm. in width by 0.18 in length. The 

 isthmus, which is almost as long and about one-half as thick as the wings, is 

 located only slightly below the median frontal plane of the medulla. Ova 

 from the same have a diameter of from 20 to 25/x. In gravid proglottides 

 where the uterus is filled with eggs only a small portion of the degenerating 

 ovary remains, and this is accommodated between the two hindermost pouches 

 of the uterus-sac. The oviduct commences in the median fine anteroventraJ 

 to the ovarian isthmus as a somewhat cylindrical oocapt, 40/x in length by 18 

 in diameter and not sharply separated from the rest of the duct (Fig. 83). It 

 passes ventrally with a diameter of 20ju for about 50,u before being joined by 

 the spermiduct, and then for only a short distance farther anterolaterally 

 along the ventral transverse musculature before meeting the common vitelline 

 duct. The latter is formed by the union in the usual manner of two vitelline 

 ducts coming from the lateral regions of the proglottis along the ventral wall 

 of the medulla. It is quite short, however, and usually contains only a limited 

 amount of yolk, its diameter being at the most only 20/x. The vitelline follicles 

 (Fig. 83) are irregularly ellipsoidal in shape, and situated either just within 

 the transverse muscles, between them and the longitudinal muscles, among 

 the latter or even slightly outside of the longitudinal muscles. While they 

 vary considerably in size and, not being very numerous, are widely spaced, 

 their average maximum diameter is about 50/i. They form a continuous band 

 completely surrounding the medulla, excepting for irregularly circular areas 

 above and below the ventral ducts and organs, in the median line, but are not 

 continuous from joint to joint. On the whole they remind one of the vitellaria 

 of A. crassum. The union of their different ductlets can be easily traced, 



