Australian Earth tvorms. 09 



part of segment 3, and to break up in segment 1. At the 

 extreme posterior end commissural vessels, supplying the ali- 

 mentary canal on the war, arise, one pair in each segment, but 

 seven segments from the end and forward for some distance 

 there are two of these vessels to the segment, probably one 

 belonging to the dorso-intestinal or tegumentarv system of 

 Bourne (11). The ventral runs forward and ends in the first 

 segment. There is no commissural between it and the dorsal 

 vessel in 13, but behind this segment one main one passes 

 round in each segment, supplying the alimentary canal on the 

 way. 



From segments 9-5 a similar vessel is found, arising as usual 

 in the case of the anterior commissurals in the hinder part of 

 the segment. In 4 this vessel does not reach the ventral one. 

 but half way round it divides into three. One branch runs 

 forward to break up definitely in segment 1 ; one back to end 

 on the posterior mesentery of 13, forming the lateral in 5, 6, 

 7, on each side, and in 8, 9, 10, 11, 12 and 13 the suh-intestinal 

 receiving in each of these segments vessels from the alimentary 

 canal wall. The third branch from the commissural m 4 unites 

 with its fellow of the opposite side in segment 4 to form a 

 short transverse vessel under the alimentary canal. 



The supra-intestinal arises from the dorsal in the posterior 

 part of 13, and runs forward to the front of 8. Three pairs of 

 hearts are present, one in each of segments 10, 11 and 12, arising 

 from the supra-intestinal posteriorly in eacli, and receiving a 

 small branch from the dorsal close to their point of origin. 



Sections. — In the region of the hearts, the blood supply is 

 seen to be fairly simple. In the hinder part of each segment, 

 on either side, the dorsal vessel sends a branch, whose opening 

 is guarded by a valve, to join the supra-intestinal, which opens 

 by a valve (Figs. 21, 22v. 23a^) into the heart (Figs. 22 and 

 23Ht.); and then runs on. giving various branches to the ali- 

 mentary canal, forming a plexus on its walls (Figs. 22 and 

 23 PI.). The heart passes to the ventral surface, and opens by 

 a valve (v.) into the ventral vessel, which is a single tube. The 

 blood from the plexus (PI.) round the alimentary canal is col- 

 lected into the sub-intestinal vessel (Sub. I.V.), which is double 

 to the end of segment 13. 



