380 KARM NARAYAN BAHL 
a specially developed mid-dorsal portion of the gut-plexus, 
and has no definite walls of its own, nor does it communicate 
directly with the dorsal vessel as it does in Lumbricus. 
In the anterior cephalized region of the body besides the 
differences in the number and position of the * hearts ’, there 
is the presence in Pheretima of an additional ‘ supra- 
intestinal vessel’ which receives all the blood from the lateral 
oesophageals and pours it into the ‘hearts’; while in the 
other two genera, the blood from the lateral oesophageals 
goes directly to ‘hearts’, and there is no ‘ supra-intestinal ’ 
vessel. 
5. Tue Course oF THE CIRCULATION OF THE BLoop. 
All observers are agreed upon the fact that the blood-current 
in the dorsal vessel has a forward direction. I have already 
stated that just in front of each septal plane, where the dorsal 
vessel is very much constricted and has the narrowest. lumen, 
there are forwardly-directed valves which, when the vessel 
contracts, prevent the flow of blood backwards. These inter- 
segmental valves, as we may call them, form an incom- 
plete circular ridge on the internal wall of the vessel at their 
point of origin; but it can easily be seen that the valves 
consist of two large dorso-lateral valves, while there are 
small dorsal and ventral ones (figs. 7 and 10). These valves 
are more or less continuous with one another, so that we can 
regard them as constituting one valve with small dorsal and 
ventral lobes and large lateral lobes. The large dorso-lateral 
lobes project forwards into the lumen of the vessel for some 
distance, and are seen as two masses lying free in the dorsal 
vessel in transverse sections. Fig. 10 (a, b, and c) shows the 
disposition of this intersegmental valve in serial sections. 
In Lumbricus, on the other hand, there are two large 
lateral valves, as shown by Johnstone (9), in the same position 
and having the same function. 
The dorsal vessel receives two pairs of dorso-intestinals 
and one pair of commissurals (‘ parietals’ or * dorso-sous- 
nerviens’) in each segment behind the fourteenth. The 
