PLATE IX. 



Figure of Medicinal Leech {Hirudo Medicinalis)^ 



Dissected so as to show its nervous, digestive, reproductive and segmental organs, 

 as seen from below ; slightly altered from Moquin Tandon's figure, pi. viii., fig. lo, 

 Monographie des Hirudin^es, 1846. 



The integuments are drawn as divided down the middle ventral 

 line, from the posterior border of the anterior sucker to the an- 

 terior border of the posterior sucker; two of the testes and two 

 of the segmental organs have been displaced outwards in the 

 segment, lettered d '^, e 2 ', the rest of the organs have been left 

 undisturbed in situ, after the fastening out of the integuments on 

 either side. 



a I . Anterior sucker, formed by the proboscidiform upper lip, 

 which is made up of four incomplete annuli, representing 

 however probably at least as many segments, and by the first 

 complete annulus surrounding the mouth. The mouth opens 

 in the middle of this sucker ; six of the eyes are carried by 

 the first, second, and third of the rays of the upper lip. 



a 2. Posterior sucker, formed by the fusion of seven distinct 

 annuli, to which seven distinct ganglia subsequently fused 

 into the single posterior ganglion of the ventral chain, 

 corresponded at one period of the animaFs development. 

 The stellate spot in the centre of the sucker must not be 

 taken as representing the opening of the anus, which is 

 situated anteriorly to the sucker in the line of constriction 

 marking it off from the posterior annuli, which are not 

 similarly modified. The anus does however open in the 

 centre of the anal sucker in Acanthobdella, as also in the 

 Polychaetous Annelid, Leucodore 



