364 KARM NARAYAN BAHL 
(figs. 1 and 2). The commissural les in the most anterior 
position in each segment, since the posterior face of a septum, 
on which this vessel lies, forms the anterior boundary of a seg- 
ment. In its ventro-lateral part each commissural vessel is 
joined by a ‘ septo-intestinal’ branch (figs. 1 and 2) which 
puts the commissural vessel in communication with the 
intestinal plexus, so that the commissural joins the dorsal 
and subneural vessels at its two ends, while in its ventral third 
it gives the septo-intestinal branch to the imtestinal blood- 
plexus. It is interesting to note the Y-shaped places of junc- 
tion (fig. 2) one comes across in sections, where the three limbs 
of the Y represent the branches of the commissural going to 
the dorsal and subneural vessels and the intestinal plexus 
respectively. All along its length the commissural vessel is 
joined by branches coming from the septal nephridia and the 
body-wall. In segments sixteen to twenty-one the com- 
missural vessel also receives the efferent capillaries from the 
prostates which get their blood-supply from the branches 
of the ventro-tegumentaries. As shown in fig. 1, I could count 
in one preparation as many as eight branches entering the 
commissural, each of these branches being formed by the 
union of several branchlets. 
The commissural vessel of Pheretima is a very interesting 
structure when we compare it with similar structures in other 
earthworms. Bourne (1) describes in Megascolex two 
vessels, which he calls ‘ intestino-tegumentary ’ and ‘ dorso- 
tegumentary ’, as follows: ‘ The main portion of the intestino- 
tegumentary vessel lies closely adherent to the body-wall just 
behind a septum, i.e. in the anterior portion of a segment ’, 
and ‘the dorso-tegumentary arises in all segments regularly 
from the dorsal vessel immediately posterior to the septum 
which forms the anterior boundary of the segment in which 
it lies’. It is clear from this description and also from his 
diagram (Pl. [X, fig. 7, in his paper) that these two vessels 
of Megascolex run in the same transverse plane, and would 
thus correspond exactly to the commissural vessel of Phere- 
tima minus its small ventral portion, since the commissural 
