72 Gtci/iineth Bacltanan : 



seem to derive their blood from the main commissural vessel 

 soon after its origin, branches passing to the nephridia on one 

 side and alimentary canal on the other, all the way down the 

 segment (compare F. ufiicus, Fig. 23, in which the nephridial 

 vessel arises from the heart). The vessel from the alimentary 

 canal on the ventral side is small and median, and opens into 

 the ventral. 



12.— Megascolex dorsal is, Fletcher. 



Perichaeta dorsalis, Fletcher, Proc. Linn. Soc. N.8.W., 

 Vol. II., 1887. 



Plate XV., Fig. 12. 



Dissection.— -The dorsal vessel is single, swollen in segments 

 11-17, joining the central by a single commissural vessel on 

 each side, at the posterior part of the body, in each segment, 

 and dividing at the anterior end into a very fine branch on 

 either side, running round to the ventral, which is here small. 

 Forward from the tail end a pair of main commissural are 

 given off in each segment, but posteriorly in segment 13 a 

 suiyra-intestinal arises from the dorsal, giving off a pair of 

 hearts at its point of origin, and runs forward to break up 

 on the alimentary canal in segment 8. In the hinder part of 

 segments 10, 11 and 12 also, a pair of hearts arise, making 

 four pairs in all, and each receives a small branch from the 

 dorsal close to its origin. In 9, 10, 11, 12 and 13 the supra- 

 intestinal gives a branch to the alimentary canal. In segments 

 9-6 a pair of commissural vessels rise from tlie dorsal, pos- 

 teriorly in each segment, and pass to the ventral, giving a 

 branch to the alimentary canal (B.A.), and ventral body wall 

 (Br.W.) on the way. In segment 5 the commissural gives off 

 a lateral one each side before joining the ventral, and this 

 lateral divides into three, one branch running forward to break 

 up, one passing under the alimentary canal to join its fellow 

 of the opposite side, and one back as the lateral, and later as 

 the suh-iufestiual, which gives a branch to the septum (B.S.) in 

 each segment from 6-12, and ending posteriorly in segment 13. 

 The sub-intestinal receives branches from the alimentary 

 canal, derived from the supra-intestinal in segments 9, 10, 11, 

 12 and 13. 



