78 Giuynneth Biuhanan : 



The ventral is single, giving off from segment 13 backwards 

 clear vessels to the ventral body wall. This form, though not 

 identical with D. yarraensis, is closely similar to it in cir- 

 culatory system, as in others (compare Professor Spencer 13). 



18. — Dipopochaeta copelandi, Spencer. 



Perichaeta copelandi, Spencei-. P.R.S. Vict., 1S92. 



Plate XVI., Fig. IS. 



Dissection . — Dorsal vessel single, swollen in segments 10-17, 

 and breaking up in segment 1. It is connected with the ventral 

 by a pair of commissural vessels in each segment, as far for- 

 ward as 14. and gives out in the hinder part of segment 13 a 

 suiyra-intestinaU which runs forward to break up in 8. From 

 the back of 10, 11 and 12 this receives a small branch from 

 the dorsal on each side, and from the junction of the two a 

 ])air of Itearts arise in each segment, or, as in most cases in 

 which there is a branch from the dorsal in these segments, the 

 hearts may be regarded as having two jDoints of origin. The 

 hearts run round to*join the ventral vessel, and from segments 

 9-5 the dorsal gives off from the back of the segment a pair 

 ©f commissural vessels, which do likewise. In 5 this vessel is 

 very small and indistinct, and in 6 it runs through a curious 

 glandular structure. In' 7 it seems to give off backwards, from 

 the middle of a similar gland, a lateral vessel on each side. 

 In 10 these become the sub-intestinal, and that of the right 

 side sends a. l)ranch to that of the left, running on for a 

 y^hort distance, and then disappearing, while the left continues 

 as the single sub-intestinal, ending in the posterior part of 

 segment 13, and receiving in 10, 11, 12 and 13, branche^^ from 

 ilie alimentary canal, derived from the supra-intestinal. 



The ventral vessel l)ecomes very small at the anterior end, 

 and does not ai)i)ear to unite with the dorsal. It gives off 

 branches to the posteiior system of the segment from 14 back- 

 wards. 



