THE GIANT EARTH-WORM OF GIPPSLAND. 15 
open the diverticula, the walls of which are formed of connective tissue, lined 
externally by peritoneal epithelium. Each process has the form of a bag, more or 
less filled with a mass of polygonal-shaped cells (y.), with very distinct nuclei; between 
the masses of these cells, often stretching from one side of the diverticulum to the 
other run strands of connective tissue. Sometimes (dv.) the processes are full of 
these cells, at others (dv.’) they are comparatively empty. The main tube (z) opens 
into the ccelom in each segment anteriorly by a slit-like aperture on its ventral surface 
just where it becomes constricted to pass with the dorsal blood-vessel through the 
septum. In this part there is very little space between the wall of the blood-vessel 
and that of the tube in question. The cells from the diverticula, which in general 
appearance, save their white colour, much resemble those of the liver of higher forms, 
can pass into the main tube and thence into the ccelom, and may perhaps serve as 
stores from which are formed the numerous white corpuscles present in the ccelomic 
fluid. The structure has no direct connection with the vascular system, nor are any 
blood-vessels whatever to be found in or about the diverticula. In a worm of some 
500 segments it could be traced anteriorly to about the 120th segment from the head 
end, where it ceased. As far as the 150th the tube could be seen, but very few 
diverticula, which were well developed from the 200th to the posterior extremity. 
°2.—Ventral Trunk. This runs, as the dorsal one, from the posterior to the 
anterior end, where, in the fifth seoment, it breaks up into small branches, distributed 
principally to the walls of the gizzard and pharynx. It lies at some distance below 
the alimentary canal (Plate 2, figs. 8 and 9; v. bv.), from which it is. suspended by a 
very definite longitudinal mesentery. It is placed just above the nerve cord, and 
passes, as usual, with this through a definite opening left in each septum in the 
median line ventrally. (Plate 5, fig. 21; sept. 0.) 
3.—Transverse Vessels. Branches are given off both from the dorsal and ventral 
trunks, and the nature and distribution of these branches differs very much in the 
; regions behind and in front of the 14th segment. (a) In the segments behind the 
14th (Plate 2, fig. 8), three branches are given off from the dorsal vessel on either 
side. Of these, one (sept. bv.) runs to the anterior face of the septum bounding the 
seoment posteriorly, and gives branches to its upper half, the other two (al. bv.) run 
round the alimentary canal, and pierce the muscular coats, forming as already 
described, two vascular networks, one on either side of the circular muscle layer. 
These may be called the intestinal vessels. From the ventral vessel arises one main 
branch on either side, close to the septum, bounding each segment posteriorly. A 
short mesentery runs out laterally from the ventral blood-vessel to the body wall, and 
serves to support on either side one of the two branches into which this lateral vessel 
divides. The upper of the two branches (sept. bv.) supplies the lower half of the 
septum ; the lower runs across the mesentery to the body wall, and supplies the latter 
with blood-vessels, and also gives off the very numerous smaller branches, which form 
such a rich plexus around the nephridia. (8) In the 14th segment the dorsal blood- 
