124, s. aoTo. 



a few sections (each = 0.01 mm.) behind, and on either side of, the 

 genital pore (PI. XV, fig. 1). The opening is wholly naked, and 

 leads into a long canal, the vaginal canal, which proceeds just on 

 the inner side of, and parallel to, the intestinal trunk, and finally 

 opens into the fore end of the paired yolk-ducts. The vaginal 

 canals are at first nearly of a uniform calibre, but very gradually 

 become larger as they approach the yolk-ducts. In GalicotyU the 

 vaginal openings lie nearly midway between the median line and the 

 lateral margins of the body, nearly on the same level with the middle 

 of the uterus. The vaginal canals, the terminal halves of which have 

 a smaller calibre than the others, proceed at right angles to the long 

 axis of the body towards the median line, where they unite with each 

 other, and form a single duct, which then opens into the seminal 

 receptacle from the antero-dorsal side (PI. XIX, fig. 1). 



In all the species of Microcotijle and Azine I have examined, the 

 vaginal opening is single, and is situated in the median line on the 

 dorsal side of the body. In most species of Microcotyle the vagina is 

 wholly naked, but in Mic. reticulata (PL V, fig. 5) and in Axine 

 heteroccrca and A. aherrans (PI. VII, figs. 5 & G; PI. VIII, fig. 4) its 

 cavity is armed with numerous, conical, chitinous spines, which are seen 

 in sections to be formed by simple elevations and transformation of the 

 direct continuation of the investing membrane of the body (PI. V, 

 fig. a; PL VIII, fig. 4). Moreover in all these species the mesen- 

 chyma around the vagina is modified into a very compact connective 

 tissue consisting of closely reticulated fibres, the interspaces of which are 

 filled with an exceedingly refractive substance, which remains wholly 

 unstained either with borax-carmin or haematoxylin (PL V, fig. 5 ; 

 PL VII, fig. 5 ; PL VIII, fig. 4). Again, in most species of Micro- 

 cotyle the vaginal opening leads into a single median canal of different 

 length according to the species, which usually proceeds straight back- 



