The South African Hirudinea. 311 



towards the aperture curving backwards, and those posterior 

 curving forwards. Further, the furrow separating annuli 35, 36 

 is not continuous, so that the thirty-fifth (35th) annulus sweeps 

 back mesially to form the anterior border of the pore. Similarly 

 the furrow separating annuli 43, 44 is incomplete, and annulus 44 

 is continued forwards mesially to form the posterior margin of the 

 aperture. That separating the thirty-fourth and thirty-fifth, although 

 continuous, is somewhat drawn backwards in the middle line. 



Sensory papillas are present on all the annuli, but are very difficult 

 to make out in the middle portion of the body. In the posterior 

 part of the dorsal surface it is seen that they are more prominent on 

 every third annulus, so that the triannulate nature of the somite 

 is definitely made out. That the sensory annulus of the triannulate 

 somite is the middle ring, as in most Glossiphoniidge with a similarly 

 constituted somite is con'cluded on the following grounds : (1) The 

 thirtieth and every succeeding third annulus as far back as the sixty- 

 third are sensory (we refer to post-cephalic annuli). (2) The genital 

 apertures, although not visible on an external examination, were 

 readily made out in longitudinal sections. The male pore was 

 found to lie between the twenty-first and twenty-second post-oral 

 annuli. Between the twenty-third and twenty-fourth annuli is 

 situated the remains of the female genital pore, as indicated by 

 the definitely prolonged furrow in the median line extending 

 towards, but not meeting, the female duct, which no longer opens 

 to the exterior directly but into the brood pouch. The genital 

 apertures in their original condition are separated then by two 

 annuli. In all Glossiphoniidae, without exception, whenever the 

 pores are separated by two annuli the male lies between somites xi 

 and xii, and the female between annuli 2 and 3 of somite xii. Since 

 this is supported so strongly phylogenetically we can safely conclude 

 that the same holds in this case. 



This indicates then that the twenty-first post-oral annulus is the 

 last annulus of somite xi ; in other words the twentieth post-oral 

 annulus, which is really the eighteenth post-cephalic annulus, is 

 sensory. This fits in with the fact that the thirtieth post-cephalic, 

 and each succeeding third annulus, is sensory and the middle annulus 

 of its somite. We can then denote the somitic constitution of the 

 genus as follows : 



Somites i-v = Head + first post-cephalic annulus. 

 Somites vi-xxvi = post-cephalic annuli 2-64. 

 Somite xxvii r post-cephalic annuli 65-66, 



