STUDIES OX THE ECTOPARASITIC TREMATODES OF JAPAN. 123 



it occupies a jxjsitiou dorsal to the vau'iua. 



The wall of the iai'g'er yolk-ducts, like ihat o(" the |)riin;rry ones, 

 consists of a thin structureless membrane wholly destitute of nuclei. 



Vagina — The xa^'ina is very ^'enerally present in the niono- 

 <^'enetie Trematodcs ; so far as I have (observed it is Avanting' only in 

 (Jctocofi/h' and ] ^irlidojilnin!. Dieckhoff" indeed descriljes it in 

 Ociohül]\riui)i huicrnldlinii ; hut from his general description of this 

 species and especially from the structure of the posterior suckers and 

 of the genital organs as described by the same writer, I doubt whether 

 this species is to be included in either of tlie two al)ove mentioned 

 genera as I shall deiine them in the systematic })art of the present 

 paper. The vagina is ])aired either throughout its whole extent, or 

 in only its jtroximal })art, or again it may be truly unpaired; in 

 most species it o[)ens by its proximal end into the yolk-duct. In 

 2Iüitocoliih\ however, it opens directly into the oviduct at the same 

 level, and side by side, with the paired yolk-ducts, so that in this 

 genus three separate ducts come to open at the same ])oint into tlie 

 oviduct. In Calicohih', again, the paired vaginal canals-^ unite with 

 each other in the median line of the body, and f )rm a short unpaired 

 duct which then opens into the rcccplaculuin sciitiitis (\\hich is in this 

 s[)ecies nothing else than an enlarged j)ortion of the oviduct) at a xavy 

 short distance from the opeuing of the unpaired yolk-duct. 



Ha\'ing thus gi\'en a general orientation I shall now proceed to 

 describe the vagina in different species. 



As I have already stsited elsewhere,''^ a tiady paired vagina is 

 present in Calicotijle and (JncliocoiijJe. In the latter genus the vaginal 

 openings lie on the ventral side of the b(jdy near the median line only 



1). Dieckhoff — Beiträge zur Keuntuiss der ectoparasitischen Trematoden. Archiv f. 

 Naturgeschichte, 57. Jahrg-., 1. Bd., 1891. p. 26i. 



2). By " vaginal canal " I mean the canal into which the vaginal opening leads. 

 3). Centralblatt für Bakteriol. u. Parasitenkunde, Bd. XIV, I8Ü3. p. 7t>S. 



