STUDIES ON EARTHWORMS. 283 
sacculated intestine, i.e., behind somite x11, two vessels com- 
municate with the dorsal trunk in each somite. One of these 
is the “intestinal branch” (d. iné.), which leaves the trunk 
near the anterior limit of the somite and passes round the wall 
of the intestine, giving off numerous branches fore and aft, 
forming a network asin Urocheta, on the intestinal wall. This 
vessel does not unite with the ventral trunk. Just in front of 
its exit from the dorsal trunk is a small valve, directing the 
blood, which passes from behind forwards in the dorsal trunk, 
into the intestinal vessel. (PIl. XVI, fig. 17, va. 7.) 
The second vessel is the “septal branch” (d. spt.) which 
comes off close to the posterior septum of the somite. It passes 
along this septum, giving off branches to it, and then reaches 
the body wall, where it joins one or more longitudinal vessels, 
which give off right and left branches and thus form a network 
on the wall (/. w.). A vessel from the nephridium joins this 
septal branch. Just behind the entrance of this septal vessel 
into the dorsal trunk is a small valve (fig. 17, va.), which pre- 
vents the blood, on contraction of the latter vessel, from passing 
into the former. The septal vessel therefore brings aerated 
blood into the dorsal trunk, whilst the intestinal branch passes 
this blood on to the wall of the intestine. 
These same two pairs of vessels are found in somite x11, 
whilst in somite x1 only the septal vessel is present. 
In somites x, x1 a branch from the dorsal trunk goes to the 
seminal reservoirs. 
In somites x, IX, VIII, VII, VI, v, and Iv, the only vessels 
which leave the dorsal trunk are the “commissural vessels” 
(com.), which pass round the alimentary tract and enter the 
ventral trunk. Of these, those in somites x, Ix, VIII, VII, and 
vi are large and moniliform, and may be specially termed 
“lateral hearts” (com’). The three posterior pairs are very 
large, but the same description applies to each. 
Each “lateral heart” leaves the dorsal trunk close to the 
posterior septum of the somite, and in the somites where the 
dorsal trunk divides into two, it arises from the undivided 
portion, and its exit is guarded by a valve (va. c., Pl. XVI, fig. 
