io8 Transactions of the Royal Canadian Institute, [vol. x. 



The common duct, which is quite short (Fig. 27) , is slightly larger than 

 the collecting ducts, and its epithelium contains relatively more nuclei. 

 It is furthermore provided with cilia, directed towards the yolk-reservoir. 



After passing for a short distance dorsally and towards either side 

 of the proglottis, depending on the arrangement of all of the ducts in the 

 generative space, this common yolk-duct expands into the vitelline 

 reservoir, an ellipsoidal or somewhat spherical sac varying from 

 25 to 55/i in diameter according to the amount of yolk it contains. Even 

 when yolk is absent, however, it is larger than the common duct and shows 

 very few cilia; thus it seems to be a true reservoir, in that it is possibly 

 differentiated early in development, and not a mere temporarily func- 

 tional dilatation. The epithelium is naturally considerably distended 

 and flattened by the contained yolk. The reservoir unites with the 

 oviduct through a short length of common vitelline duct whose structure 

 is identical with that of the above-mentioned portion. 



The vitelline follicles, like the testes, are situated in the 

 medullary parenchyma, that is, within the longitudinal muscles and 

 consequently within the nerve-strands (vide supra), thus resembling, as 

 to situation, those of the genera, Ancistrocephalus Montic, and Anoncho- 

 cephalus Luehe, (Luehe, '02). There they form a continuous cylinder 

 from one proglottis to the next, enclosing the excretory ducts and repro- 

 ductive organs, including the testes, but broken ventrally and dorsally 

 by middle fields corresponding in extent to the region occupied by the 

 generative ducts, that is, from the anterior end of the cirrus-pouch to the 

 posterior end of the ovary (Figs. 17, 18 and 19). Posteriorly they 

 crowd the ovarian limbs very closely, a few even passing above and below 

 their hinder ends. Thus, in extent, the vitelline follicles are comparable 

 to those of Cyatliocephalus (Kraemer '92), Schistoceplialus (Kiessling 

 '82), and Bothriocephalus dendriticus Nitzsch and B. ditremus Crep. 

 (Matz '92), excepting that in the three latter forms the dorsal middle- 

 fields are occupied by them, while in the first genus neither dorsal nor 

 ventral middle-fields are left free of follicles. In D. latus, on the other 

 hand, both fields accommodate no vitelline follicles (S. and L. '72). 



The follicles themselves are usually spherical to ellipsoidal in shape; 

 but in ripe joints, where they are very closely packed together, the out- 

 line is somewhat polyhedric. Furthermore, they vary greatly in size, 

 the smallest being only about 8/z in diameter, while the largest, which are 

 more numerous, are even 50/i. The yolk-cells also vary in size, being 

 from 5 to 15/X in length, obviously owing to their relative states of 

 maturity. This is shown in Fig. 29a, which also gives some idea of their 

 variety of outline. The latter, however, seems to be the result of the 

 accommodation of a number of semi-fluid bodies within a fairly tense 



