HIRUDO — THE LEECH. 21 



cylindrical or flattened, varying according to the state 

 of contraction. The body is dark (blackish or grayish 

 with brownish stripes). It is marked by a series of 

 rings, at least loo in number. The dorsal surface is 

 mottled by distinct rows of spots, whereas the ventral 

 surface is irregularly mottled. At both ends of the body 

 the worm is provided with a mouthpiece or sucker. 



Fig, I. — Leech (Moeller). 



With the posterior one the animal fastens himself, and 

 then brings the triangular mouthpiece into play. This 

 is provided with three sets of tooth plates, which by their 

 muscular attachments move like a segment of a circular 

 saw and make a triangular cut into the skin, through 

 which the animal sucks the blood by means of its muscular 

 pharynx. The clotting of the blood is prevented by a 

 locally secreted ferment. The blood passes into a large 



