188 



T I'd ii.<ftcl ions. 



The iiephridiiim is .suj)plied hy two vessels — one connected with the 

 dorsal, the othei- with the ventral, blood-trunk (fig. 12). The former trunk 

 gives origin to a dorso-jiarietal veSKel. which courses down the body-wall, and 

 at a little distance below the lateral line divides into three branches — («) to 

 body-wall, {h) to septum, and (c) to the nephridium. The venti'al system 

 is built up on the same plan. It is inadvisable to use the names " afferent "' 

 and ■■ efferent" in regard to these vessels, for although no doubt one of 

 them takes blood to the organ and the other one takes it away, yet we are 

 in ignorance as to which does which. A comparison of the literature on 

 the matter shows that Harrington* and Bourne agree to differ from the 

 views expressed by Benham for LHmhricxs. The statement of the latter 

 as to the coui'Se taken by the blood in the dorso-parietal and ventio-parietal 

 vessels is diametrically opposed to the views of Harrington, who made a. 

 most careful and elaborate study of the vascular system in LxDibricus. 



On the other hand, the only earthworm which agrees with Maon'drihus 

 ill being without a sul)ueural blood-vessel in which the vascular system ha,s 

 been pretty fully described is Microchaeta (Benham), and in the disposition 

 of the vessels it agrees quite closely with Maorldrilus. So far, however, as 

 the course of the vessels on the nephridium are concerned, we do not know 

 the details. But in MaoridriJits the arj'angement of the nephridial vessels 

 is so similar to those in LiuHbriciis that it is unnecessary to reproduce 

 the figures wdiich 1 prepared for 'uiy thesis, ft will suffice to give a brief 

 account, and a ligui'e representing the 

 origin of the vessels in transverse section 

 (fig. 12). 



The nepliridial vessel arif,es from the 

 dorso-parietal vessel, and runs alongside 

 the septum towards the ventral end of the 

 nephridium, where it enters the "spur""; 

 it divides into two or three branches, one 

 of which traverses the " folds " to reach 

 the '■ dorsal lobe." Here it breaks up 

 into a mass of small vessels (capillaries), 

 which Subdivide again and again so as to 

 cover the winding ducts, and then unite 

 to enter a corresponding vessel connected 

 with the ventral blood-trunk. This vessel 

 lies par llel \vith the fomier. Similarly, 

 the olhei' bi-ancheS referred to, which go 

 to the spui' and to the outlet-duct, divide 

 into capillaiies, all of which enter corre- 

 sponding vessels connected with the ventro-parietal vessel. 'J'his passes 

 through the septum at the level of the nephrostome, and thence ])asses 

 to the ventral blood-trunk. 



There is a great fascination in tracing out the capillaries of this elal)orate 

 blood-Supply, because it is remarkably Ijeautiful under the microscope, and 

 because, on account of the parallel arrangement of afferent and efferent 

 vessels, one may be traced with ease into the other. Perhaps I may be 

 permitted to quote here a sentence from Boui'ne (15, p. 327) which Seemed, 

 as I read it, so ]>eculiarly applicable to Maon'drilxs. Speaking of the peri- 

 pheral vascular netwoi'ks of Moniligaster grandis, he says, " Perhaps the 



(!. 12, — Diajivani of the blood- 

 supply to the nephridia in all 

 ])arts of the worm with the exccji- 

 tion of the most anterior ones. 



* Harrington, " The Calciferous Glands of the Earthworm, with Appenflix on tlie 

 Circulation." Journal oj Morphology, siippl. to vol. 15, 1899. 



