JAPANESE LAND LEECHES. 289 



the IbllowiDo- regions; cepbilic, clitellar, median, anal, and acetabular. 

 These five regions are also recognisable in the case of Orohdella, but as 

 the boundary between them can not be fixed but arbitrarily, I thought 

 it better not to adopt Apathy's method strictly. In tlie following, the 

 external characters of the three species of () roh del la will be treated succes- 

 sively from the head end toward the acetabalum, without patting there- 

 by any accurate boundary between the regions above mentioned. 



Head. There is no distinct line of limit that separates the head 

 region from the rest of the body. As in all Gnathobdellids, this 

 region passes by insensible gradations into the clitellar region, but we 

 may regard, perhaps, the head proper as ending with the rings that 

 form the posterior margin of the mouth. The triangidar portion of 

 the body that lies in front of the eyes was counted, in the diagnosis of 

 the species, as the first ring, although not considered as such by some 

 authors (Blanchard, Whitman). The second ring is characterised in all 

 the species by the presence of two distinctly visible, yet inconspicuous, 

 eyes; this makes it very probable, that the second ring is homologous 

 throughout. The third ring is very broad in OvohdcUa Whitmani and 

 is divided into two unequal portions by means of a transverse furrow ; 

 the anterior ])ortion is as l)road as the fourth ring, while the posterior 

 is only of half that breadth. This ring of OrohdeUa Wliitmani seems 

 to correspond to the third and fourth rings of OrohdeUa Ijimai. The 

 fourth ring of OrohdeUa WhUwani and the fifth ring of OrohdeUa Ijimai 

 have two minute black dots, situated near the lateral margins of the 

 body and representing rudimentary eyes. When viewed from under- 

 neath, the head region looks nearly the same in all the species. The 

 whole ventral surface of this region as far as the fifth, sixth, or seventh 

 ring, according to the species, is occupied Iw a wide mouth, much 

 like the same organ of C i/licohdeUa or LiuiihricohdeUa in Kennel's 

 figures (1886). The two rings that form the posterior boundary of 



