324 ALFRED GIBBS BOURNE. 
Its walls are muscular throughout its length, and in the 
anterior segments the ccelomic epithelium covering it becomes 
pigmented; this is more especially the case near the septa 
and at the sides. 
It is nowhere much dilated, but is largest in Segments 
vi—1x, and constricted in the region of Septa v-v1, vi-vII, 
vil-vil1, and viti-1x (the thick septa). In front of Septum 
v-v1 it very rapidly narrows, and becomes a mere thread on 
the surface of the pharynx where it dips down among the 
salivary glands. It does not appear to have any special mode 
of termination at this anterior end, but simply loses itself in 
a fine capillary network. 
It presents a series of valves (fig. 39) as in Megascolex 
ceeruleus.! The valves are placed in the septal regions and. 
prevent any backward flow. There are also valves (mentioned 
below) at the orifices of the dorso-intestinal vessels. 
It is never double in any part of its course. 
Posteriorly it ends by dividing into a pair of dorso-tegu- 
mentary branches. 
Ventral Vessel.—(Fig. 27, V. V.) This is also known as 
the subintestinal or supra-neural vessel. 
Its walls are thick and strong, but are formed of connective 
tissue and not muscle. 
There are no valves in the ventral vessel. 
It is of uniform calibre for the greater portion of its length, 
but posteriorly it gets very gradually smaller and smailer, 
while anteriorly it narrows rapidly in front of the hearts. 
It comes to an end anteriorly and posteriorly by dividing 
into a pair of branches in each case, those at its anterior 
extremity lying on the subesophageal ganglion. 
Supra-intestinal vessels are absent. 
Ty phlosolar Vessel.—No such vessel exists, there being, 
as I have stated above, no typhlosole. 
Latero-longitudinal and Subneural System.—In- 
testino-tegumentary vessels, i. e. vessels carrying blood between 
the peripheral capillary networks and the intestinal capillary 
Cf. Bourne, ‘Quart. Journ. Micr. Sci.,’ vol. xxxii, Pl. ix, fig. 12, A, 
