THE MEDICINAL LEECH 



variable, but in Britain usually consists of a greenish background 

 with a pair of longitudinal red stripes and a pattern of irregular 

 black markings nearer the lateral margins. The ventral surface is 

 usually black with white and grey markings. 



The body of the leech, exclusive of the posterior sucker, is 

 divided by transverse furrows into 102 annuli. A typical mid-body 

 segment comprises five annuli but towards the extremities of the 

 body the number per segment progressively decreases. The distri- 

 bution of the annuli between the prostomium and body segments 

 is as follows: 



Grand total 102 



The anterior sucker is a depression on the ventral surface of 

 segments I-IV, and at the base of the depression lies a small trira- 

 diate aperture, the mouth. The prostomium forms the anterior 

 border of the sucker and may be turned back ventrally, thus 

 partially closing the oral aperture. The posterior sucker is a 

 muscular disc, approximately circular in outline, which is a more 

 powerful organ of adhesion than the anterior sucker. It is clearly 

 marked off from the body and is made up of seven fused segments. 

 The anus is a very small aperture in the mid-dorsal line near the 

 junction of the body and the posterior sucker. 



The male pore lies between annuli 31 and 32, while the female 

 pore lies five annuli further back between 36 and 37. The male 

 pore is the more conspicuous and may be used as a guide to the 

 position of the female pore. During the breeding season the 

 glandular clitellum is visible on annuli.26-40. The nephridiopores 

 are found in segment 7 between annuli 14 and 15, and between 

 the second and third annuli of the following 16 segments. They 

 are very small indeed, and the best way of finding them is to 

 squeeze gently a freshly narcotized specimen, when a little fluid 

 will be exuded from the nephridial bladders. 



There are three principal kinds of sense organ on the surface 



