GENERAL ANATOMY OF THE LEECH. 165 



" intestine " originates, and runs backwards on the median 

 line of the body. It is much smaller than the " stomach," 

 tubular and muscular. 



7 . Near its posterior end the intestine dilates to form an 

 ovoidal colon. 



8. From this a very small and short rectum runs to the 

 dorsal anus, which lies between the last aunulus and the 

 sucker. 



c. Cut the digestive tract at the anus, and at about the 

 middle of the pharynx, and carefully dissect it away and 

 remove it, to expose the organs which lie below. On the 

 inner surface of the ventral body-wall, notice : — 



1. The median ventral nerve-cord, made up of : — 



(i.) A series of ofanglia; one' in each of the somites 

 except those at the anterior end of the body. These 

 ganglia give rise to lateral nerves which may be traced out 

 into the body-wall. 



(ii.) The commissures which join these ganglia into a 

 chain. 



2. Tlie ventral blood-vessel, a transparent tube which 

 surrounds the nervous system, and sends off lateral 

 branches. 



3. The two lateral blood-vessels, running along the 

 sides of the body, 



4. The segmental organs ; a row of eighteen pairs of 

 convoluted tubular organs, one for each somite of the body, 

 situated just inside the lateral vessels. Each of these 

 is connected with a transparent membraneous globular 

 vesicle. 



5. The male reproductive organs. 



(i.) About one-sixth of the length of the body from the 

 anterior end the globular muscular penis will be seen. It 

 is prolonged into a siphon-shaped tube, which oj^ens exter- 



