T. B. ROSSETER ON DREPANIDOT.ENIA VEXUSTA. 21 



thickly on each margin of the proglottis. Some are oval whilst 

 others are circular with concentiic lamellae ; seen in sections they 

 measure, the former 0*010 mm. by 0*013 mm., the latter have 

 a diameter of 0*010 mm. 



When the looped vas deferens within the vesicula seminalis has 

 been filled with spermatozoa, then, and then only, does copulation 

 take place. During the secretion of the spermatozoa the cirrus 

 has remained within the sheath b?low the annular orifice. This 

 filling of the vas deferens has the effect of pressing it, owing to 

 its swollen condition, closely against the walls of the pouch, which 

 causes the circular and longitudinal muscles of the pouch, and 

 the proximal retractor muscles, which are attached to them, 

 to^ stretch to their utmost. When the vas deferens is filled to 

 repletion they suddenly contract, and this sudden contraction 

 of the proximal retractor muscles shortens the pouch, forces out 

 the cirrus in an upward, though somewhat curved dii'ection, 

 dragging with it the neck of the vas deferens, and consequently 

 the vas deferens as well, for the looped vas deferens is per 

 fectly free within, and independent of the pouch ; and at times 

 when fully exserted a portion of the sheath is extruded with the 

 cirrus. Once above the cloacal orifice, the cirrus bends downw^ards 

 and inserts itself into the vaginal orifice. This sudden contraction 

 of the muscles of the pouch, pressing against the distended vas 

 deferens, forces up the sperm, causing it to run up the cirrus and 

 enter the vaginal canal. It then runs dow^n the annulated 

 efferent duct, and fills the receptaculum, where it is stored up 

 for the fertilisation of the ova. When the vas deferens is emptied 

 of its contents the act of coitus is complete, and the cirrus with- 

 draws itself, by the retraction of the elevator muscles from the 

 vagina, back again into the sheath. Von Linstow thinks that 

 " once the act of copulation has taken place, the cirrus does not 

 return again into its sheath " ; such, however, is not my experience 

 with Drejy, venusta, excepting when the sheath has been extruded 

 with the cirrus. I find in those ripe segments which were 

 ready to separate themselves from being an integral part of 

 the strobila — and it is on these segments I have made my 

 observations respecting the development of the ova — that, when 

 all the other male organs have become absorbed, the chitinous 

 cirrus is not extruded, but is drawn completely back into what 

 remains of the sheath. So far as it applies to Brej). venusta, one 



