14 ON THE ANATOMY OF MEGASCOLIDES AUSTRALIS, 
formed immediately beneath these. From this network branches pass down, piercing 
the layer of circular fibres (Fig. 5), and another network is formed at the bases of 
the columnar cells, amongst which branches penetrate. The intestine is covered 
externally with an epithelium of cells, whose extremities, facing into the body cavity, 
are much larger than their internal ends, which run down between the longitudinal 
fibres. Still finer processes can at times be traced on from these cells, leading 
through the layer of muscular fibres till they reach the intestinal epithelium (these are 
represented too clearly in the figure). Hach cell contains in its swollen end a great 
number of minute yellow-brown granules, which give the characteristic colour to the 
intestine in this part. The nucleus is very distinct, somewhat spherical in shape, and 
placed where the cell begins to narrow. In the very median dorsal line these cells 
are absent, and a tubular structure is present, connected with the wall of the alimen- 
tary canal, and surrounding the dorsal blood-vessel, to which reference will be made 
later on. The brown cells are merely special modifications of the peritoneal 
epithelium, with which they are directly continuous around the dorsal tube just 
mentioned. There is nothing corresponding to the typhlosole, nor to the intestinal 
glands present in certain earth-worms. 
5.—Vascular System. The vascular system is, in comparison with most earth 
worms, somewhat simply developed. It consists of the following vessels :—(1) dorsal 
trunk ; (2) ventral trunk; (8) transverse vessels; (4) lateral vessels. As- in 
Pleurocheta, Pericheta, Pontodrilus, and Microcheta, there is no sub-neural trunk. 
1.—Dorsal Trunk. ‘This runs from the posterior to the anterior end of the body, 
in close connection with the dorsal wall of the alimentary canal. In the fifth segment 
it breaks up into numbers of small branches, which run forward and form a plexus in 
the walls of the gizzard and pharynx. (Plate 1, fig. 2; plate 2, figs. 8 and 9, 
d, bv.) In segments 14-6 inclusive, it is somewhat swollen and its walls more 
muscular, and hence firmer than in the posterior region. 
In Plate 4, fig. 20, is a drawing representative of a structure confined to the 
hinder half, or even less, of the body. Such a structure does not appear to have been 
described in any other earth-worm as yet, and its exact nature is very doubtful. 
When the hinder part of the body is opened, the dorsal blood-vessel is seen to be 
surrounded by a white-coloured tubular structure, from which more or less solid 
diverticula are given off on each side. (Plate 4, fig. 20; plate 2, fig. 5, , and dw.) 
In the section (Fig. 5), half of the tubular structure surrounding the dorsal blood- 
vessel is represented. It is lined throughout by the peritoneal epithelium (ep.), 
which in the median line, as mentioned above, is not modified into brown cells, 
though certain of the cells lying nearest to these become somewhat columnar. The 
walls of the tube are formed of connective tissue (ct.), in which lie a certain number 
of circularly disposed muscle fibres, which, where the tube rests upon the alimentary 
canal, pass both towards the central line, lying upon the longitudinal fibres, and 
outwards for a short distance amongst the bases of the brown cells. Into the tube 
