Australian Earth wo nns. 65 



4. — Megascolex tenax, Fletcher. 



Perichaeta tenax, Fletcher. P. Linn. 8oc., N.S.W., 

 vol. ii., 1887. 



Plate XIV., Fig. 4. 



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

 10-15, and joining the ventral by a commissiiral branch on 

 each side, supplying the alimentary canal on the way, at the 

 posterior end of the body. The dorsal and ventral vessels are 

 thus connected as far forward as segment 14, there being no such 

 vessel in .segment 13. From the hinder part of eacii segment, from 

 9-5, a pair of commissurals arises, and in 9, 8, 7, and 6 each 

 gives off marked branches to the ventral body wall (Br.W.), 

 in some cases from a distinctly swollen patch, which probably 

 has a propelling function (cf. similar structures in M. goon- 

 murk). A well-marked vessel arises from the dorsal on each 

 side in the posterior part of segment 4, but does not reach the 

 ventral, dividing instead inio two, one of which runs forward 

 to segment 1, in which dorsal and ventral also break up ; and 

 the other passes as a lateral through segments 5, 6, 7, 8 

 and 9, and as a suh-intestinal through 10, 11, 12 and 13, end- 

 ing in this last. Small vessels, only running a short distance 

 down and then breaking up, arise from the dorsal in segments 

 2 and 3, forming the anterior network of the dorso-tegumentary 

 of Bourne. A supra-intestinal vessel arises from the dorsal in 

 the posterior part of segment 13, and runs forward to the front 

 of 10. From this branches are given off on each side, supplying 

 the alimentary canal, in segments 10, 11, 12 and 13, and join- 

 ing the sub-intestinal on each side on the ventral surface. In 

 10, 11 and 12 heart'< also arise from the supra-intestinal, one 

 pair posteriorly in each segment, and pass to the ventral 

 vessel — the anterior pair being not very conspicuous in the 

 specimen examined. 



The ventral vessel is single, running the whole length of the 

 body, and joining the dorsal at the anterior end by a very fine 

 branch. 



