HIRUDO. 195 



the crop the blood is slowly passed into the stomach and 

 digested as required. 



The student will have noticed already in cutting open 

 the leech (by a dorsal incision) that the interior is very 

 different from that of Arenicola. There is no spacious 



^ . coelomic cavity ; the organs have to be picked 



out and the skin peeled off. This is due to 



the fact that the coelom is filled up almost entirely by 



Fig. 123. — Magnified View of Two Consecutive Segments 

 OF THE Leech (loth and nth). {Ad nat.) 



Nerve Cord in 



Ventral Sinus. 



Penis jjulled in 



from exterior. 



Epididymis. 



Ovisac. 



connective tissue, the only parts of this cavity which are left 

 being (i) a median dorsal sinus or space, (2) a median 

 ventral sinus surrounding the nerve-cord, and (3) a few 

 small spaces lying immediately over the testes. 



The blood-vascular system is complex and the blood- 

 _, . „ , vessels have definite walls. There are two 



Blood- Vascular. . , , ^ ^ • ^ - rr 



main lateral vessels which give oii num- 

 erous smaller branches. These communicate with a 



