522 



ANNELIDA. 



twisted, and gives off branching ductules just before reaching the capsule 

 (Fig. 422). 



In Hirudo the internal opening is a 

 large structure, and is sessile upon the 

 capsule (Fig. 422) ; it is divided up into 

 several ciliated spoon -shaped openings, 

 and has the usual syncytial character. 



In Hirudo mcdicinalis there are 17 pairs 

 of nephridia ; the first one is in the seg- 

 ment of the 2nd free ganglion, the last 

 one in that of the 18th ganglion. The 

 first six are without internal funnels ; 

 the remainder, the first nine of which 

 are in the segments of the testes, and 

 the last two in the segments behind the 

 testes, possess internal openings at the 

 end of the testis-lobe. The testis-lobe is 

 a process of the nephridium which pro- 

 jects towards the middle line, and in the 

 testis segments abuts upon the testis. 



ff 



A B C 



FIG. 423. Diagrams of the nephridia. A, of 

 PontoWella (two contiguous nephridia are 

 shown) ; E, of Hirudo ; C, of Clepsine. a, a 

 capsules and funnels ; b-c canal in testis lobe ; 

 c-e canal in main lobe ; d in Hirudo, canals in 

 caecal end of the "main lobe"; e-g in Hirudo 

 ducts in the apical lobe; g the apex; c-l, in 

 Clepsine, and g-l, in Hirudo, unbranched canal 

 passing to the external aperture ; j-fc, in 

 Hirudo, the vesicle ; x, x caecal ductules in 

 Pontobdella. (After Bourne.) 



r 'J- 



y.is. 



y.sa 



FIG. 424. Diagram illustrating the 

 arrangement of the renal, generative, 

 vascular, and nervous organs of 

 Hirudo medicinalis (from Perrier, after 

 Bourne), cer.g. passage of the oeso- 

 phagus through the nerve-collar ; cp 

 epididymis ; g. 1-S3 the ventral gan- 

 glia ; gl. glandular dilation of oviduct : 

 l.v. lateral blood vessel ; l.L, Lab., l.d. 

 branches of the same; neph., or n. 1-17 

 the 17 pairs of nephridia ; oe circum- 

 oesophageal commissure of the left 

 side ; ov ovary ; pe penis ; te 1-9 the 

 9 pairs of testes. 



