152 ILLINOIS BIOLOGICAL MONOGRAPHS [440 



by Linton, especially in the dorsal half, the inner layer of circular fibres being 

 much more numerous ventrally. Thus there is left a comparatively large 

 space aroimd the ejaculatory duct to accommodate the retractor muslces 

 and a small amount of parenchyma the nuclei of which are situated peripherally 

 much as in B. scorpii. A character which distinguishes this species, however, 

 from others of the genus is the presence of a loosely arranged bundle of muscle - 

 fibres attached to the ventral end of the cirrus-sac and passing downwards be- 

 tween the coils of the uterine duct, beyond which they do not seem to have any 

 definite attachment. Since the myoblasts and nuclei of these fibres are quite 

 prominent, especially some distance from the cirrus-sac, the whole bundle 

 has something of the appearance of an elongated gland. The protruded cirrus 

 has a maximum length of SS/x with a diameter of 30/i. This everted condition 

 of the cirrus, taken in conjunction with the nature of the genital cloaca de- 

 scribed above, and the fact that there is no vaginal sphincter, points strongly 

 to the cross-fertilization of at least different proglottides, rather than to self- 

 fertihzation. The former would, furthermore, seem possible between con- 

 tiguous segments, since in many cases two consecutive cloacae were found close 

 together and at the bottom of an apparently temp>orary depression of the dorsal 

 s\irface. 



The vagina has no sphincter, but begins somewhat broadly, as shown in 

 Linton's figure 5, only to narrow down quickly to about 5/i half way along its 

 course, which is almost straight ventrally. It expands slightly before joining 

 the oviduct but does not form more than a temporarily functional seminal 

 receptacle. The ovar}% much compressed anteroposterior^, is from 0.5 to 

 0.6nmi. wide by only 40/x long at the isthmus, and from 0.13 to 0.18mm. deep. 

 Its limbs are entire but much disturbed in their course laterally by the uterine 

 ducts of contiguous proglottides. The oocapt has an average diameter of 

 25//. Beyond it the oviduct enlarges, after constricting as usual, to about 

 25m again where it is joined by the vagina. At the latter point there is a vesti- 

 bule as in the last species. Just beyond this the oviduct is joined by the com- 

 mon vitelline duct which is enlarged near the jimction to form the yolk reservoir 

 or "central vitelline mass," about 45/i in diameter. The vitelline follicles 

 are very numerous and closely arranged in the cortex in two lateral fields, leav- 

 ing a broad median strip free of them on each surface of the strobila. Their 

 maximum lengths, breadths and depths are 25, 60 and 115m respectively; 

 they have thus approximately the same bulk individually as those of B. manu- 

 briformis. They are continuous at the edges of the strobila and occupy the 

 central one-half of the thickness of the cortical parenchyma, excepting in the 

 median free strips. While the rather small shell-gland occupies a somewhat 

 limited position dorsally at the level of the ventral end of the cirrus-pouch, 

 the uterine duct takes so many coils, all of which are filled with eggs, in the 

 median portion of the proglottis on both sides of the midline that most of the 

 other structures are all but obUterated — at least at first sight. Both the uter- 

 ine duct and the uterus-sac are arranged pretty much as in B.manubrifarmis; 

 but the latter is only from 0.27 to 0.37mm. wide by about 0.15 long and about 



