62 Gtrynvdh. Buch(tna)} : 



In segments 10, 11, and 12, there are no commissural vessels 

 arising from the dorsal, but behind this, one main one arises 

 on each side about the njiddle of the segment, and runs down 

 to join the ventral one, sending" branches to the alimentary 

 canal on its way. In segments 9, 8, 7, 6 and 5 there are com- 

 jnissural vessels arising from the dorsal. That in segment 4 

 does not reach the ventral, but runs back as far as segment 9 

 as the lateral. In segnients 10, 11 and 12 this receives a 

 branch from the plexus on the alimentary canal, forming a 

 SI ih- intestinal on each side. 



The ventral vessel is single, and runs forvrard to the first 

 segment, breaking up there. In segments 6, 7, 8, and 9 the 

 vessels connecting it with the dorsal give out marked branches 

 to the ventral body-wall before joining it. The supra-intes- 

 tinal vessel arises from the dorsal posteriorly in segment 12, 

 and runs forward to the front of 8. It gives off three pairs of 

 hearts in 10, 11 and 12, and in these segments also are marked 

 branches to the alimentary canal arising from the supra-intes- 

 tinal and running round to join the sub-intestinal. Professor 

 Spencer (15) describes six pairs of hearts in segments 6-12. His 

 anterior ones are evidently in this as in other cases, those I 

 have called anterior cdimnissural. 



Section x.— l\i^ blood sujiply in one segment in the region 

 of the hearts, a> rL'construcTed from serial sections, is seen to 

 be complicated. At each mesentery the double dorsal vessel 

 unites to form a single one. At the point of junction a valve 

 (Fig. 20 V.) is formed, and the vessels there divide again. In 

 tlie hinder ]»ai-t of each segment the supra-intestinal unites 

 with the vessel forined by the union of the two hearts of the 

 segment, at which jioint a valve is placed : and the supra-in- 

 testinal runs forward u^ the next segment, giving off marked 

 vessels to the abmcnt.uy canal, on whose walls is formed a 

 close plexus. 



The ventral vessel in each segment receives the heart, the 

 junction ])eing guarded by a valve, and just ])efore the point 

 of union a branch is given off to the ventral body wall and 

 nephridia (Fig. 20, Af. Ne) - tlie veutro tegiuneut;i,ry of Bounu', 

 A short distance up, the heart, wliic-h is here luucii smaller 

 in section thiin on tlie dorsal surface, w-;ves otf from a valved 



