]^(^() s GOTO. 



differences of my view from that of the last mentioned writer, and I 

 shall now proceed to explain it more at length. 



Let LIS in the first place consider the vagin;i of the Monogenea. 

 So far as I know this organ is truly paired only in Onclwcotyle, 

 Calicoiijk, Pohjstomum^ and Sphjranura. In the first two genera its 

 external opening is situated on the ventral side of the body, while in 

 the other two «enera it is situated on the lateral mari^ins. In Calico- 

 tijle it opens into the oviduct, but in all the other three genera it be- 

 comes continuous with the yolk-duct. In Microcotijle, Axine, and 

 Hexacotijle the vaginal opening is situated on the dorsal side in the 

 median line of the body (or sometimes on the lateral margin as in 

 Axine hclones iicGovding to Lorenz); but that the vagina in these 

 forms has been derived from a truly paired one seems to me beyond 

 doubt. Thus, in Axim lietewcerca the vagina immediately divides 

 right and left into two canals, which proceeds backwards, keeping 

 symmetry Avith respect to the median line of the body ; in Microcotijle 

 reticulata, M. chiri, 31. tnuicata, and in Hexacotijle the vagina remains a 

 single duct for a certain distance in the median line of the body, but then 

 divides into two canals ; in M. fusiformis, M. caudata, and some other 

 species of the same genus the vagina remains single for a longer dis- 

 tance ; in Microcotijle sciacnae the paired vaginal canals unite with and 

 separate from each other twice during their course; while finally in Axine 

 aherrans the vagina remains single throughout its whole extent, and 

 opens into the fore end of the unpaired yolk-duct. Lorenz'^ in one 

 place figures the vagina in Axine helones as opening directly into 

 the oviduct, Init in another figure (fig. 2) he represents it as 

 opening into the yolk-duct. Considering his figures alone I 

 should trust the former firrure as showing more details ; but 



1). /. c.-Taf. I, fig. 4. 



