288 



ASAJIRO OKA: ON SOME NEW 



Gifa (Nawa) and in the Hakone mountains. The specimen from Gifu 

 shows the tendency toward a farther division of the rini^s much more 

 distinctly than the other two which were hroug-ht from Hakone. 



E.x tenia I Morp hologij . 



It is very interesting to notice that the three species described 

 ahove h ar a striking reseml^lance to each other in external features, 

 in spite of the great difference in the ninnl)er (^f the rings. The position 

 of the eyes and the genital orifices is coincident in all the species. The 

 number of ring's that intervene between those bearing thegenitiil orifices 

 is different according to the species, but if we disregard the external 

 rino's and take only the somites into consideration, these openings are 

 found to be situated in the corresp(jnding portion of the corresponding 

 somites. In the Figs. A, 1), & C (PI. XXIX.) I have tried to show 

 the relatitjn of the rings to the soinitcs, in the different species, which 

 might be summed up in tabular form as follows : 



Or. Whitmani Or. Ijimaï Or. octonaria 



I- VI somites l:^ rings 17 rings Springs 



VII-XXIII „ 17x4= (il „ 17x6 = 102 ,, 17x8 = 130 „ 

 XXIV-XXVl „ 8 „ 10 „ 13 „ 



Total number SS „ 129 „ 171 „ 



Although the body of Oroldella apj)ears to bave a uniform struc- 

 ture throughout its whole length, except at the acetabulum, we can 

 still recognise in it, by careful examination, a certain number of 

 regions. These are not, in fact, so appju'ent in our leeches as in some 

 other f<)rms, such as BrnncheUion and Ozohranchv:^, in which some of 

 the regions are easily distinguishable externally, but jis they present 

 differences not only with regard to the internal organisation, but also 

 to the constitution of tlie somites, they must be treated separately in 

 the consideration of the external morphology. 



Apathy (1888) and Lang (1891) divide the body of a leech into 



