MEDICINAL LEECH. 



229 



ous branches which riddle the spongy body, and have a 

 definite muscular coat. On the dorsal surface and ventrally 

 around the nerve-cord are two lacunar spaces, which are 

 really portions of the true body cavity, and not parts of the 

 vascular system, ^"ith those and similar spaces, however, 

 the blood vessels are connected by means of a secondarily 

 developed series of canals, roughly corresponding to the 

 lymphatic vessels of Vertebrates. The blood is red, and 

 contains colourless floating cells of diverse form. 



FIG. no. A nephridiuni of leech. After Bourne. 



F., Internal terminal funnel ; C., glandular coil covered with blood 

 vessels ; V., external terminal vesicle. 



Excretory system. - There are seventeen pairs of 

 excretory tubules or nephridia, from the second to the 

 seventeenth segment inclusive. These open laterally on the 

 ventral surface, voiding the waste products extracted from 

 the blood vessels which cover their walls. From the seventh 

 to the seventeenth, each nephridium ends internally in a 

 ciliated " cauliflower lobe," corresponding to the funnel of 

 Oligochseta, and enclosed in a blood space, apparently part 

 of the reduced ccelom. In the first nine of these funnel- 



