140 S- GOTO. 



very distinctly (Pi. XII, fig. 6); and on the -posterior surface of the 

 penis the membrane seems to be changed to a certain extent into a 

 chitinous nature; for here it remains wholly unstained with haema- 

 toxylin and has all the optical properties of a chitinous substance. In 

 Cdlicotyle (PI. XIX, fig. 7) the atrium genitale is reduced to a very 

 small cavity communicating with the exterior by a comparatively 

 large pore, and the greater part of it forms merely a sheath for the ex- 

 ceedingly long, chitinous penis already described. In Monocotyle it is 

 more spacious and opens to the exterior by a somewhat small pore; 

 but the greater part of its cavity is almost completely taken up by the 

 penis (t*]. XVIII, fig. 3). The external membrane of the body is also 

 in this case clearly seen to be continued into the genital atrium; here, 

 however, it becomes very much thinner and compact, and loses its 

 granular character. 



In all the species hitherto considered the genital atrium receives 

 both the vas deferens and the uterus, so that it may without any 

 impropriety be called the genital cloaca; but this is not the case in 

 some species of the next genus as will presently be seen. 



In Tristonium as well as in Epibdella the genital atrium is 

 an elongated, more or less tubular cavity with a very small 

 external opening. Into it the penis projects; and in most species 

 the uterus opens into it, but in some species, as in T. rotundum 

 and T. ovale, this opens independently to the exterior, so that the 

 cavity can not be called the genital cloaca. In Epibdella ovata it is for 

 the greater part of its length tubular, but is enlarged towards its ends 

 to make room for the penis (PI. XXVI, fig. 6). The uterus opens 

 into it between the tubular and the enlarged portion. In E. Ishilcaiuae 

 the whole atrium is more or less tubular in accordance with the 

 greater length of the penis; and the uterus opens on the top of a low, 

 conical papilla, a short distance behind the middle of the length of 



