388 KARM NARAYAN BAHL 
again—so that the blood-flow is not self-sufficient in one 
segment ; the blood must circulate in the whole body. 
In the first thirteen segments (fig. 5) the blood-system is 
different, and so is the course of blood. The dorsal vessel is 
no longer a receiving channel; it has no dorso-intestinals 
and commissurals opening into it and feeding it with blood—in 
fact it receives no blood at all, but behaves instead as a great 
arterial trunk, pumping out all the blood it has received in its 
posterior region. Of course the greater part of its blood, 
together with the whole of the blood in the supra-intestinal 
vessel, is pumped into the ventral vessel through the two pairs 
of ‘ latero-intestinal hearts’ in the twelfth and thirteenth 
segments. But a quantity of blood flows forwards anteriorly 
and this is pumped into the ventral vessel by means of the 
‘lateral hearts’ of the ninth and seventh segments, and is 
supplied to the gizzard and the pharyngeal nephridia by the 
‘hearts’ in the eighth and fourth, fifth and sixth segments, 
until the dorsal vessel ends by branching on the pharyngeal 
mass. In accordance with the change of function of the dorsal 
vessel we have the change in the disposition of the valves. 
In this region there are no valves projecting into the lumen 
of the dorsal vessel; on the other hand, the valves are present 
in all the ‘ hearts’ at a little distance away from their origin 
from the dorsal vessel. ‘These valves point in the direction 
away from the dorsal vessel, and lead the blood from the dorsal 
vessel outwards, preventing any blood taking the reverse course. 
There are also valves at the distal ends of the * hearts ° (fig. 11) 
which allow blood to flow out of ‘hearts’ during systole, 
but do not let the blood come back during diastole. The dorsal 
vessel is therefore a distributing channel here; most of its 
blood it pumps out into the ventral vessel for distribution, 
but a small quantity it distributes itself to the gizzard, the 
pharyngeal nephridia and the pharynx. 
With regard to the flow of the blood in the ventral vessel, 
I agree with Bourne (1, p. 77) in thinking that the blood coming 
from the ‘ hearts’ flows both forwards and backwards. There 
are no valves in the ventral vessel preventing blood from flowing 
anteriorly, and in addition to the ‘ hearts’ of the twelfth and 
