58 



THE BIOLOGY OF AN ANIMAL. 



Besides the lateral vessels from the sub-neural and supra-neural a pair 

 of " ventro-lateral " (y.Z., Figs. 26 and 27) are given off in each somite from 

 the sub-intestinal to the nephridium, probably receiving from it the blood 

 Rrhich originally entered through a branch of the dorso-tegumentary. 



ST 2/: 7 



im 



JTITV. 



Fig. 27.— Nephridia of JjumbiHcns. A showing the regions of the tube, B the vascular 

 supply. /, II, III, the three principal loops. 



.4. /, funnel; n.t, the "narrow tube"; m.t, middle tube; u\t, wide tube: m.p, mus- 

 cular tube or end-vesicle ; ds, dissepiment. The narrow tube extends from a to g 

 and is ciliated between a and ft, at c, and from d to c. The middle (ciliated) tube 

 extends from g to h, the wide tube from h to k, where it opens into the muscular 

 part ; eX, external opening. 



B, Letters as before ; d.t, dorso-tegumentary vessel, bringing blood from the dorsal 

 vessel, receiving at s a branch from the body- wall, sending an afferent branch to 

 the nephridium, and finally joining the sub-neural (s.n); v.l, ventro-lateral vessel 

 carrying the blood from the nephridium to the sub-intestinal or ventral vessel 

 (s.i) ; v.v, ventral nerve-cord. (After Benham; the direction of the blood-cur- 

 rents according to Bourne.) 



Excretory System. It is the office of the excretory system to 

 remove from the body proper the waste matters ulthnately re- 



