500 



ZOOLOGY 



SECT. 



funnel : it has a great number of small ciliated openings into the 

 sinus in which it lies. In most of the nephridia (all except the 

 first six pairs) modified 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 blood-system containing, like that of 

 the Earthworm, red blood, the plasma coloured with hemoglobin 

 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. 



FIG. 416. Nephridium of Hirudo medicinalis. a. I. apical lobe ; d. vesicle-duct : 

 m. 1. middle lobe ; np. nephridiopore ; nst. ciliated funnel ; r. I. recurrent lobe ; 

 I. I. testis-lobe ; vs. vesicle. The communication here represented as existing between 

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



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

 414 and 417, 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. 



The two principal sinuses are respectively dorsal (Figs. 412 and 

 417, d. s.) and ventral (v. s.), the former lying just above the 

 enteric canal in the middle dorsal line, the latter occupying a 

 similar position on the ventral side, and enclosing the ventral 

 nerve-cord. The two sinuses are in connection with one another 

 posteriorly, and are also in communication, by means of their 



