218 Proceedings of the Royal Society of Victoria. 



11. 

 12. 

 13. 

 14. 

 15. 

 16. 

 17. 

 18. 

 19. 

 20. 

 21. 

 22. 

 23. 



Acetabular 



3 

 c3 eS 



Oka^ states that " Apathy and Lang divide the body of a 

 leech into the following regions : cephalic, clitellar, median, anal, 

 and acetabular." In Philiemon it is alniost impossible to fix 

 such divisions, as there is no strict line of demarcation between 

 these parts, the one passing by insensible gradations into the 

 other. 



The head region may be considered to extend back to the 

 posterior margin of the mouth and consists of the first nine 

 annuli, that is somites I.-V. It carries the five pairs of eyes — 

 the position of which has already been described — and the 

 anterior sucker. This occupies nearly the whole of the ventral 

 surface, the upper lip being formed of the part lying immediately 

 in front of the first pair of eyes, and the lower lip of the 5th 

 and 6th annuli, which are less distinctly separated on the ventral 

 than on the dorsal side. In the anterior sucker lies the mouth, 

 and attached to it are the two jaws. These are placed latero- 

 ventrally and in some contracted specimens can be seen pro- 

 tuding from the anterior sucker. They are situated in somite V. 

 Following on the head region are three somites which may be 

 regarded as forming the neck, the first .somite, VI., being the 

 last abbreviated segment at the anterior end. 



So far I cannot distinguish a clitellar region. Microscopically, 

 as well as externally, there appears to be not the least difference 



1 Loc. cit., p. 288. 



