JAPANESE LAND LEECHES. 299 



Morpliologij of the first ring. That part of the body lying in front 

 of the externally visible pair of eyes consists of one ring in Orohdella. 

 This ring is however in reality the product of coalescence of a certain 

 number of rings. That this apparently single ring is composed of at 

 least two rings is very clearly shown by the position of the first pair 

 of rudimentary eyes (Fig. 1, PI. XXX). The well-developed pair of 

 eyes of Orohdella corresponds, tlius most probably to the first pair of 

 eyes of Xerohdella Lecomtei (LS92) and to the second pair of Hœmadipsa. 

 In auch f^rms as the members of Hirudinea, where the metameric 

 structure of the body is modified at both ends in consequence of the 

 division of labour, the number of the rings counted in those parts is 

 only descriptive and should not be looked u])on as data for ascertaining 

 the homology of the rings. 



Comparison with other land-leeches. 



All the genera of land-leeches, including Orohdella^ may be arrang- 

 ed in two groups, namely, the one containing Hœmadipsa^ Mesohdella, 

 Xerohdella^ and the other containing Gylieohdella, Lumhricohdella, and 

 Orohdella. The leeches of the first group are characterised by the 

 presence of toothed jaws and l\y the semi-parasitic mode of life. They 

 have well developed acetabulum and 4-5 pairs of eyes, that are dis- 

 tinctly visible externally. The second group contains, on the other 

 hand, all those forms destitute of jaws. They live in moist localities, 

 such as under fallen leaves and mosses or amcrngf rotten wood, and 

 hunt after earthworms. The acetabulum is small or entirely wanting. 

 There is only one pair of distinct eyes or none at all. 



If we compare Orohdella with Hœmadipsa, we see at once how 

 the different mode of life works differently on the general form of the 

 body. The one living upon trees and dropping unperceived on per- 

 sona or animals that pass under them, has a comparatively small and 



