Australian Earthivornis. 73 



The ventral vessel is single, occurring the whole length of 

 the body. 



13. — Digaster excavata, Fletcher. 



Penissogastep excavata, Fletcher. Proc Linn. Soc, 

 N.S.W., 1888. 



Plate XV., Fig. 13. 



Dissection. — Dorsal vessel single, swollen in segments 13-15, 

 less so in 12-10, and running forward to segment 1, where it 

 divides into two, one branch running round to each side to 

 join the ventral. From 19 backwards the dorsal sends a co77i- 

 jfiissural to join the ventral in each segment, supplying the 

 alimentary canal on the way, but from 18-14 there are two of 

 these branches to the segment. In segment 13 the dorsal is 

 not connected with the ventral at all. but gives off at the 

 posterior mesentery a su pra-intestinal , which runs forward to 

 the end, apparently lilindly, in the front of 8. Posteriorly in seg- 

 ments 10, 11 and 12 a pair of hearts arise, each having a 

 double origin — from the dorsal and supra-intestinal vessels 

 — and runs round to the ventral. In segments 9-4 the 

 dorsal gives oft a commissural on each side in the 

 under part of the segment, passing to the ventral, 

 and giving a branch to the ventral body wall (Br.W.), 

 and back septum (B.S.) in 9-5, and in 8-5 one to the alimentary 

 canal (B.A.). That in segment 4 gives rise to the lateral. 

 which runs back as the suh-intestinal, and also, apparently, 

 forward to break up in the salivary gland, but both this and its 

 junction with the commissural vessel in segment 4 are indis- 

 tinct, owing to the large development of this sland. The sub- 

 intestinal remains distinct on each side, and runs back to 

 segment 16, giving branches to the posterior septa of segments 

 13 and 14 (B.S.). It receives in 9. 10. 11, 12 and 13 vessels 

 from the alimentary canal derived from the supra-intestinal. 

 The ventral is single along its whole length, breaking up in 

 segment 1, and receiving, as described, a branch from the 

 dorsal in this segment. 



