STUDIES ON EARTHWORMS. 285 
Thus, in the dorsal trunk, the greatest contractile region is in 
somites vii1 and 1x, whilst the only direct communication 
between it and the ventral trunk is by means of the seven pairs 
of ‘commissural vessels,” of which the posterior five pairs 
are contractile. 
(6) The Ventral Trunk.—This longitudinal median vessel 
commences anteriorly, either by the union of the two circum- 
pharyngeal branches (dr.) of the dorsal trunk, or in a network 
formed by their subdivision. It passes directly backwards (V.) 
lying rather nearer the nerve-cord than in Lumbricus, and 
has much more muscular walls than the dorsal trunk has: 
after receiving various branches, it enlarges in somite x, and 
remains much the same size throughout the body. 
In somites Iv, V, VI, VII, VIII, Ix and x it receives the 
ventral ends of the commissural vessels, near the posterior 
boundary of the somite in each case (com. com’.). 
In somites x and x1 branches leave it, to go to the seminal 
reservoirs (v. ¢.), and in all of the somites a pair of vessels passes 
from the ventral trunk to the septum (v. spt.), and supply a 
branch to the nephridium. Behind somite x1 three or four 
small vessels in each somite from the wall of the intestine 
(v. int.) enter the ventral trunk. 
(c) The Lateral Trunks.—In the anterior somites of the 
body a longitudinal trunk is seen on each side (L.), lying close to 
the alimentary tract and rather ventrad of it, passing below the 
sides of the gizzard. These “ lateral longitudinal ” trunks have 
no direct communication either with the dorsal, or with the 
ventral trunk, thus differing from the pair of lateral longitudinal 
trunks in Lumbricus, which arise as branches from the dorsal 
trunk. Hach lateral trunk rises from a vascular network on the 
pharynx (nw. ph.) and ends posteriorly in a network on the intes- 
tinal gland of somite 1x (nw. int.). In each somite, through which 
it passes, it receives a small vessel from the posterior septum 
(2. spt.), and a vessel from the alimentary tract (J. al.) ; this is 
usually small, but in somite viii a large vessel from the gizzard 
enters the lateral trunk. 
The direction of the blood in these lateral trunks is difficult 
VOL, XXVi.—NEW SER U 
