130 ILLINOIS BIOLOGICAL MONOGRAPHS [418 



The vas deferens fonns a very compact mass of coils lateral to the cirrus- 

 sac and extending from the utenis-sac ahead to the wing of the ovary on that 

 side behind. It alternates irregularly from right to left, as does the greater 

 part of the uterine tube which occupies a similar position on the other side of 

 the cirrus-sac. In states of moderate contraction of the proglottis it is about 

 0.22imn. in length, 0.16 in width and 0.18 m depth. Inmiediately within the 

 cirrus-sac the vas deferens continues as a thin-walled senainal reservoir, sUghtly 

 coiled and occupying approximately the ventral one-third of the former. It 

 varies from 35 to 80/x in diameta:, but in the sections made it was found to 

 contain only a comparatively small number of spermatozoa. Beyond this 

 receptacle the duct narrows down to about 5/i in diameter and continues as 

 the ductus ejaculatorius with many coils, situated in the proximal one-third 

 of the sac alongside the seminal reservoir even when the cirrus is protruded. 

 This portion of the duct very graduaUy enlarges as its circular muscle fibres 

 become more numerous and its lining thicker and thicker as it merges into the 

 cuticula of the cirrus proper. The latter is about 5m in thickness and deeply 

 "cleft," or, to be more precise, broken up into a great nimiber of coral -like 

 villi by means of irregular i eparate pittings reaching almost to the base of the 

 tissue. The duct may here (at the middle of the cirrus-sac) attain a diameter 

 of 2Sn. The cirrus proper is somewhat conical when protruded (Fig. 102) and 

 has a TnaTiTniim length and width of 130 and 85m, respectively. However, on 

 account of the similar structxire and large diameter (25/*) of that part of the 

 duct still invaginated \sithin the sac one is led to think that the organ may 

 reach a much greater length — ^with probably a considerably smaller diameter. 

 From the tip of the cirrus to the inner end of its duct, where the cleft cuticula 

 stops and which point might well be the f imctional tip of the organ, it is at least 

 0.28mm. in length. Thus it would seem that the organ functions as a very 

 eflScient and powerful intromittent organ. The cirrus-sac is ovoid in shape and 

 comparatively large, being about 250^ in depth (length of longitudinal axis, 

 which is directed dorsoventrally), 180^ in length and 210 in width, when the 

 cirrus is not protruded, and thus somewhat flattened in the longitudinal axis 

 of the strobila. Its wall is only about 2.5m hi thickness, and composed of very 

 fine muscular fibres the direction of which was not determined with certainty. 

 The contents of the sac consists of a loose parenchymatous tissue, containing 

 many nuclei and numerous retractor muscle fibres. The nuclei, which are 

 situated close around the duct and are comparatively nimierous, are in all 

 probability myoblastic in their nature. The retractor fibres pass obUquely 

 upwards and inwards from all points of the wall to their points of attachment 

 to the cuticula of the cirrus. This attachment is seen very nicely when the 

 cirrus is protruded (Fig. 102), for then the fibres are much elongated and theycan 

 be followed even to the evaginated cuticula. Their myoblastic nuclei are quite 

 easily distinguished, especially in the everted portion of the cirrus. The cirrus- 

 sacs are all in the median line, their longitudinal axes being almost constantly 

 in the median sagittal plane. 



