Leeches. 



6 9 





on the surface, but can easily be distinguished within, 

 as the organs of the body are arranged in successive 

 groups. Leeches have 

 at their front end a 

 sucker, and some have 

 a second suctorial 

 disk at the hinder ex- 

 tremity, and several 

 species are even pro- 

 vided with lateral 

 suckers. The mouth 

 is generally situated in 

 the front sucker, and 

 it is armed with three 

 horny jaws or plates 

 (fig. 41) with serrated 

 edges. These plates 

 act as teeth, enabling the leech to make incisions in the 

 skin of its host through which to suck the blood. 

 The digestive canal is straight and consists of a central 

 tube with a row of eleven blind pouches along each 

 side (fig. 42, B) which can become distended, hence 

 the body can take in a great quantity of blood. 



There is a pair of nerve-ganglia in each segment 

 of the body ; the first (fig. 42, c) of these is compara- 

 tively large and made up of several smaller ganglia 

 grouped together ; the successive ganglia are united 

 into a chain by fine filaments, and they lie on the 

 ventral or under side of the digestive organs. 



Leeches possess proper blood-vessels in which 

 their own nutritive fluid circulates. Their water- 

 vascular system takes the form of a series of scgmental 



Reproductive organs of leech. B Di- 

 gestive canal of leech. C Nervous system 

 of Malacobdella. The two cords are 

 more separate than in other species. 



