HYMESOLEPIS XITIDA, KRABBE, AND II. NITIDULANS, KRABBE. 35 



of the vagina, but only the exterior convexity of the spines. The 

 efferent duct of the vaginal canal is turned towards the expulsion - 

 bladder, hence the cirrus-pouch. In a specimen accidentally 

 crushed, this minute organ was tilted up from its recumbent 

 position, and I was thus enabled to obtain a measurement of the 

 diameter of the orifice — viz. 0*009 mm. This interesting organ — 

 which was apparently unobserved, possibly owing to its minute- 

 ness, by both Berg and Krabbe, as the latter makes no reference 

 to it in his text — I consider to be a distinguishing characteristic 

 of the female genitalia in the strobilation of II. nitida and 

 II. nitidulans. The vaginal canal, on leaving the vagina, runs 

 diagonally upwards ventral of the expulsion-bladder, and makes 

 a junction with the receptaculum seminis. This is a large sub- 

 globular vesicle situated in the middle, somewhat anteriorly, of the 

 segment, and has a diameter, when extended with spermatozoa, 

 of - 108 mm. In the segment it has the appearance of a light- 

 refracting monocle, and bulges up on either side like a biconvex 

 lens. When the segment is sul -jected to the influence of carmalum 

 and methyl-blue, although the cellular tissue and the various 

 organs are contrast-stained, this sperm receptaculum, which is 

 but faintly coloured, stands out like a circular pane of coloured 

 glass. 



Of the 153 species of avian tape- worms described by Krabbe 

 there are but few instances in which he refers to the cirrus- 

 bladder, and only three in which he describes this organ as 

 being "staerkt lysbrydende," or " strongly refracting the light " 

 — viz. T. villosa, II. nitida, and //. nitidulans. The hooks on the 

 rostellum of T. villosa are distinctive of that species, and cannot 

 be mistaken for those of the other two ; and, although the 

 cephalic hooks of //. nitida and H. nitidulans resemble each 

 other in formation, and are numerically the same, yet the con- 

 trast in their size (H. niti<7<(, 0*1] mm., and U. nitidulans, 

 0'054 — 0*057 mm.) is so great that it gives to each species a 

 distinctive character. In the present case, in the absence of the 

 scolex and hooks, the " lysbrydende " organ enables me to define 

 this species of tape-worm as Krabbe's T. nitida ; and, readily 

 as one can understand Krabbe calling it a "lysbrydende" or 

 light-refracting organ, yet he fell into a grievous error in 

 denominating it the cirrus-bladder or pouch, as it is the female 

 and not the male sperm vesicle. 



