STUDIES OX THE ECTOPAEASTTIC TREMATODES OF JAPAN. 127 



In Monocotijle, Triatomiim, and Epihdella the vagina is present 

 onl}' on the left side of the body, and opens to the extei-ior on 

 the ventral surface. In Monocotijle the vaginal opening is situated 

 close to the left trunk of the intestine, about midway between the 

 por?(.s genitalis communis and the anterior end of the ovary, and is sur- 

 rounded by a compact tissue exactly similar to that described in Hexaco- 

 iijlc ; but there are no muscular fibres (PL XVII, fig, 1). It leads 

 into a short canal which soon opens into a large spherical cavity, the 

 receptaculum seminis ; from the other end of this a canal proceeds 

 backwards, and opens into the oviduct at the point where the 

 latter receives the paired yolk-ducts. In Tristomnm the vaginal open- 

 ing is situated a short distance behind tlie opening of the genital atrium, 

 in some species more towards the lateral margin, but in others nearer 

 the middle line. In most species the opening is surrounded more or 

 less with the compact tissue so often mentioned in other genera ; but 

 this is in most species very inconspicuous. The vaginal canal makes 

 in this genus numerous complicated windings in its course ; 

 and at various distances from the external opening according to 

 the species it is swollen to a considerable size and is filled with 

 sperm mass — forming the receptacitluin- seminis. Beyond this the 

 vaginal canal contracts into a very fine canal, which then opens in all 

 the species I have observed into the yolk reservoir (PL XXI, fig. 8; 

 PL XXII, fig. 5; PL XXIII, fig. 8; PL XXV, figs. 3, 8, & 8), and 

 not into the oviduct as is stated by Monticelli'' to be the case in 

 Trist. uncinat'um. 



From the above it is evident that the seminal receptacle in 

 Tristomum and Monocotijle is nothing else than a part of the vaginal 



1). MonticelK— Tristomum uuciuatum, n. sp. Boll. d. Soo. di. Xat. in Xapoli. An. Ill, fasc. 

 II, 1889. 



