512 



ZOOLOGY 



the testis. This lobed body is a modified ciliated funnel : it has a 

 great number of small ciliated openings into the sinus in which 

 it lies. The nephridia of the Leech differ from those of the 

 Earthworm, and also from those of Nereis, in the absence of 

 any internal openings, and in the absence of cilia in the interior 

 tof the canals. In most of the nephridia (all except the first 

 six pairs) ciliated funnels are present attached to the inner 

 ends of the nephridia, but these do not open into the canals of 

 the latter. 



There is a complex vascular system, containing, like that of 

 the Earthworm, red blood, the plasma coloured with haemoglobin 



Pig. 409.— Nephridium of Hirudo medicinalis. a. I. apical lobe; to. I. middle lobe"; 

 np. nepliridiopore ; list, ciliated funnel ; r. 1. recurrent lobe ; t. 1. testis-lobe ; vs. vesicle ; 

 vs. d. vesicle-duct. The communication here represented as existing between the ciliated 

 funnel and the nephridial canals does not occur. (After Bourne.) 



and containing sparsely distributed colourless corpuscles. But a 

 striking difference from the preceding annulate types is found in 

 the fact that the blood-containing spaces are of two kinds — blood- 

 vessels proper, having muscular walls ; and blood-sinuses, the walls 

 of which are devoid of muscle. 



The two principal blood-vessels are lateral in position (Figs. 

 407 and 410, I. v.), running fore and aft at the level of the middle 

 of the nephridia and uniting with one another at the anterior and 

 posterior ends of the body. They send off branches both dorsally 

 and ventrally, some of which anastomose with one another. The 

 ultimate branches break up into capillaries in the integument, 

 nephridia, &c. 



