SttJDIES Ox THE ECTOfARASlTrC TREMATODES OF JAPAN. 139 



many species o£ Microcolijle. Of Axine triangularis (PI. Vll, fig. 7) I 

 have had only a single specimen, and therefore could not make sagittal 

 sections of it; but judging from analogy and from a comparison of pre- 

 parations of it in toto with those of others, I believe the genital atrium 

 of this species to be very nearly similar to that of M. chiri already 

 described (PI. V, fig. 4). There is a hemispherical organ on the 

 dorsal side of the atrium exactly similar in form to that of M. chiri, 

 and the internal surface of which is covered with slightly recurved, 

 conical spines (PI. VII, figs. 7 & 8). I have not been able to see 

 distinctly the opening of the vas deferens; but I believe it lies as 

 in M. chiri, and not therefore m the hemispherical organ — again 

 relying in so doing on analogy. 



In Octocotyle the genital atrium is somewhat vase-shaped, with a 

 short narrow neck which opens to the exterior. It receives at one of its 

 sides the uterus, and the chitinous spines of the penis project from the 

 base of its cavity (PI. IX, fig. 12). In Diclidophora, on the other hand, 

 the genital atrium has a wide opening to the exterior, almost of an equal 

 diameter with the atrium itself (PI. XI, fig. 4). It sends out backwards 

 a tubular prolongation which becomes continuous with the uterus, the 

 boundary line between the two being in this case especially hard to deter- 

 mine. On the dorsal side, the main cavity of the atrium communi- 

 cates by means of a minute pore with a somewhat cone-shaped side-cavitj', 

 into which the chitinous hooks of the penis project (PL XI, fig. 4). In 

 Hexacotyle the genital atrium communicates with the exterior by 

 means of a short, tubular canal formed by the thickening of the lips of 

 its external opening (PI. XII, fig. 6). As a whole it is a tolerably 

 spacious cavity; but all its central part is occupied by a large conical 

 papilla — the homologue of the penis — on the top of which opens the vas 

 deferens. In this genus the direct continuation of the external invest- 

 ing membrane of the body into the genital atrium can be observed 



