Structure of (in Australian Lcmd Leech. 223 



the dorsal surface to the posterior extremity where it opens at 

 the anus (Fig. 4). 



The anterior sucker, as already described, occupies the whole of 

 the ventral surface of segments I. -IV. Its upper lip is formed 

 from the prostomium and is set with marginal lip organs (Fig. 8). 

 The ventral lip consists of the 5th and 6th annuli. The sucker 

 is muscular, and by its means the leech attaches itself to its prey 

 for pui-poses of feeding. The comparatively large cavity behind 

 this may be regarded as the buccal chamber (B.C.) or mouth — 

 the opening from it into the pharynx being the oral aperture. 

 The pharynx wall is muscular and made up of three folds, one 

 median dorsal (D.F.) and two latero-ventral (L.F.). Growing up 

 -as continuations of the latero-ventral folds are two muscular jaws 

 which project into the buccal chamber — a jaw corresponding to 

 the median dorsal fold not occuring. Tlie position of the jaws is 

 seen in Fig. 9. 



They have the appearance of somewhat rounded disc-like 

 structures, the free edge consists of a thickened cuticle (cut. 

 Fig. 10) forming a definite ridge. Along tliis ridge can be seen 

 a distinct groove, in which are placed some seventy or moi'e small 

 denticles (D.). The denticles are not placed contiguously, and 

 the groove between any two teeth appears to be to a certain 

 extent closed in or filled up with tissue. This gives the appearance 

 of the tooth being set in a little socket (Fig. 11). The denticles 

 are conical, and curved slightly towards the mid-ventral line, 

 the rest of the surface of the jaws is smooth and covered with 

 the cuticle. It can easily be seen from sections (Fig. 11) that 

 the jaws are exceedingly muscular orgaiis with numerous glandu- 

 lar structures between the denticles (Fig. 12 gl.). There is 

 little doubt that these glands resemble those of Hirudo medicinalis 

 described by Croockewit.^ The glands are unicellular, with 

 long, narrow, waving ducts, which open on the free edge of the 

 jaw between the denticles. The nuclei of these gland cells 

 can be seen in many of the preparations. 



1 Zool. Anzei^v., vol. xvi., 1S93. 



10 



