VASCULAR SYSTEM OF PHERETIMA OTO 
communicate dorsally with the supra-intestinal vessel, while 
ventrally they are connected with the lateral-oesophageal 
vessels. They might have been ealled ‘ intestinal hearts ’ but 
for the fact that these ‘loops’ do not pulsate, have non- 
muscular walls unlike those of the ‘ hearts ’, and I believe that 
the flow of blood in them is from the lateral oesophageals to 
the supra-intestinal, a fact which I refer to again below. On 
these considerations I exclude these vessels from the category 
of ‘hearts’ and call them ‘anterior loops’, since they have 
nothing in common with the so-called ‘ hearts’ and ‘ anterior 
loops ’ in greater detail below ; they are shown in fig. 5. 
Thirteenth and Twelfth Segments.—lIn each of 
these two segments there is a pair of ‘ latero-intestinal ’ hearts. 
In systematic accounts of the genus Pheretima it is only 
these two pairs that are described, and no mention is madeé 
. of the anterior pairs of ‘ hearts’. Even if the term ‘ hearts ’ 
be restricted to those commissures which communicate with 
the ventral vessel below it should include the ‘ hearts ’ of the 
seventh and ninth segments. This diagnostic character for 
the genus Pheretima is thus generally erroneously described, 
and the genus should be recognized to possess at least four 
pairs of ‘ hearts’, two ‘ lateral’ and two ‘ latero-intestinals ’. 
The ‘ hearts ° of the twelfth and thirteenth segments (fig. 5) 
are situated in the posterior parts of these two segments, and 
their walls are intimately attached to the septa behind them. 
They have thick muscular walls and a spacious cavity, and at 
their dorsal ends communicate anteriorly with the supra- 
intestinal and posteriorly with the dorsal vessel. At the 
places where the branches from the dorsal and supra-intestinal 
meet to enter the ‘heart’, each has a pair of valves leading 
to the ‘ heart’, and similarly there is a pair of valves at the 
ventral end of each ‘heart’ just above the place where it 
joins the ventral vessel (fig. 11). The dorsal valves prevent 
the blood from going back to the dorsal or supra-intestinal 
vessels during systole, while the ventral valves prevent the 
blood from entering the ‘heart’ from the ventral vessel 
during diastole. 
