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



Each testis is surrounded by a very thin membrane which is directly 

 continuous with the wall of the vas efferens (Fig. 20), a point which is 

 rather difficult to make out since the testes are packed closely together and 

 the vasa efferentia anastomose freely between them. Numerous, even 

 about ten, developing cytophores in various stages may be seen in the 

 younger testes. 



The anastomoses of the vasa efferentia are best seen in the 

 vicinity of the posterior end of the vas deferens (Figs. 17, 21 and 22) and 

 not so well, among the testes laterally and in the interproglottidal regions. 

 Thus it is conceivable that sperms developed in testes situated in the 

 regions between the sets of genital ducts may find their way to the vas 

 deferens of the same proglottis or to that of the proglottis ahead or behind, 

 as the case may be. This would be facilitated by the rupturing of the 

 delicate walls of the testes, which alone separate them in ripe joints, to 

 form larger and more accessible channels for the sperms. Many instances 

 of such ruptures were seen in the serial sections studied. Sommer and 

 Landois ('72) found that the testes in the anterior part of the proglottis 

 of Dibotkriocephalus latus (Linn.) passed their sperms to the 

 vas deferens of the joint ahead, but these relations were not found 

 in this species in spite of the otherwise general resemblance between the 

 arrangement of the genital ducts of the two. The vasa efTerentia, them- 

 selves, vary considerably in diameter and possess very thin walls in 

 which scattered and flattened nuclei are situated, as observed by Lonn- 

 berg ('91) in Bothriocephalus rugosus (Batsch), (Figs. 20 and 21). 



Just ahead of the uterine opening the vasa efferentia unite to form a 

 rather indefinite sperm reservoir, directly continuous with the 

 posterior end of the vas deferens (Figs. 17, 21 and 22) and thus resem- 

 bling the similar structure of many Bothriocephalids. Its walls are 

 intermediate, as to the structure of the epithelium, between those of the 

 vasa efferentia and those of the vas deferens (Fig. 21). The anterior 

 boundary of the sperm-cistern is marked by the position of the foremost 

 of one to three separate vasa efferentia which join the vas deferens on 

 that side towards which the latter is directed in development (vide infra) ; 

 rarely do vasa efferentia empty into the vas deferens ahead of this short 

 region. 



While it was found impossible to determine the lengths of the sper- 

 matozoa in sections, it was noticed that their anterior ends were 

 differentiated as quite long and narrow cylindrical heads, slightly larger 

 in diamenter than the rest of the sperm, evidently pointed at their an- 

 terior ends and graduated less abruptly towards the tail. These heads 

 stain very densely with Heidenhain's Iron-Haematoxylin and are con- 

 sequently quite easy to pick out, while the other parts are scarcely dis- 

 cernable in the masses to be seen in various portions of the male ducts. 



