102 Transactions of the Royal Canadian Institute. [vol. x. 



The cirrus-sac is situated about midway between the dorsal 

 and ventral surfaces of the proglottis, immediately ahead of the vesicula 

 seminalis (Figs. 17 and 38). In shape it is spheroidal, being flattened 

 laterally and somewhat protracted ventro-posteriorly where it follows 

 the cirrus to the latter' s opening, as the following measurements indicate: 

 longitudinal diameter, 0.16 to 0.21 mm.; transverse diameter, 0.14 to 

 o. 16 mm.; vertical diameter, o. 18 to 0.20 mm. 



The wall of the cirrus-pouch, although quite thin, is wholly muscular 

 and composed of two sets of fibers which can be better distinguished as 

 such in younger proglottides than in older or gravid joints where they 

 course irregularly and obliquely. Of these two sets the inner are circu- 

 larly disposed while the outer are arranged longitudinally, thus corres- 

 ponding to the description, by Sommer and Landois, of the parts in 

 Dibothriocephalus latus. The fibers in the postero-dorsal portion 

 of the wall intermingle with those of the vesicula seminalis; 

 postero-ventrally they converge towards the opening of the cirrus, 

 around which, with the dorso ventral parenchymal fibers of the immediate 

 neighbourhood, they attach to the cuticle of the ventral surface. A 

 very few fibers, on the other hand, difficult to distinguish from these 

 dorsoventral parenchymal muscles, pass from the dorsal wall of the cirrus 

 to the dorsal body-wall. Thus retraction of the cirrus, if, indeed, it is 

 ever everted, would appear to be brought about by the mere elasticity of 

 its tissues and of those surrounding it. 



The dorsal half to two-thirds of the space within the cirrus-sac, which 

 accommodates the ductus ejaculatorius and its expansion, the second 

 vesicula seminalis, is filled with numerous parenchymal cells grouped 

 irregularly around the duct outside of the fine longitudinal muscular 

 fibers following the course of the latter. The myoblastic nuclei of these 

 are visible as spindle-shaped, highly-staining bodies, closely applied to 

 the fibers themselves. The ventral half to one-third of the space, on 

 the other hand, appears much more compact in sections and transparent 

 preparations, since it is in this region that the large retractor fibers of the 

 cirrus are located. The latter are arranged in groups (Fig. 24) and 

 attached evidently to the cuticle centrally, while they intermingle 

 peripherally with the fibers composing the wall of the sac. The myo- 

 blastic nuclei are related to these fibres as in the case of the longitudinal 

 muscles of the parenchyma, that is, one nucleus is associated with three 

 or four fibrils. In addition to the circular fibers situated immediately 

 outside of the cuticle of the cirrus proper, there are other finer ones to be 

 seen for some distance beyond the cytoplasmic area, above-mentioned, 

 intermingling with the large retractor fibers (Fig. 24) . 



