THE COURSE OF THE BLOOD FLOW IN 
LUMBRICUS. 
J.B. JOHNSTON AND SARAH W. JOHNSON. 
ALTHOUGH this form is almost universally used as a type for 
laboratory study, its circulation is still very imperfectly under- 
stood. The present contribution aims to give a better under- 
standing of the course taken by the blood, as determined by 
observation and experiment upon large specimens of Lumbricus 
terrestris. The following brief review of the anatomy of the 
circulatory system, which is well understood, will serve as a 
basis for the discussion of the blood flow. 
A large dorsal vessel extends along the dorsal surface of the 
intestine from the caudal end of the worm to the pharynx, over 
which it ramifies. Strong pulsations of this vessel run in 
more or less regular succession from the posterior to the 
anterior end. In somites VII to XI, inclusive, five pairs of 
circular vessels, the strongly pulsating %earts, encircle the 
esophagus, connecting the dorsal vessel with the ventral. 
The ventral is a longitudinal trunk lying beneath the intestine 
and giving branches to the body wall and the nephridia. A 
subneural and two lateral neural vessels constitute, by reason of 
an irregular. network of anastomoses between them, a connected 
system accompanying the nerve cord. This system is connected 
through branches of the lateral neurals with, the body wall. 
Connecting the dorsal and subneural vessels are the so-called 
parietals. They occur, one pair in each segment beginning 
with XII, close behind the septa and give off branches to the 
body wall and the nephridia. The parietal in somite XII is 
much larger than the others. In each somite two or more 
unpaired ventro-intestinal vessels enter the wall of the intestine 
from the ventral vessel, while two pairs of dorso-intestinals pass 
from the dorsal vessel into the wall of the intestine. 
os oe 1 From the Zoólogical propion of West Virginia University. 
