348 ALFRED GIBBS BOURNE. 
must be borne in mind that the flow is here a continuous one 
while in the arteries it is intermittent. 
The arrangement of the vessels in a segment of M. ophi- 
dioides shown in fig. 28 emphasises my view as to the direc- 
tion of the blood flow, such as it is, in the dorso-tegumentary 
vessels. The dorso-intestinal vessels on the gizzard wall have 
a characteristic arrangement which is here shown. 
Generalisations with regard to the Vascular System 
in Earthworms. 
IT am now in a position to offer some wider generalisations 
with regard to this system than I was when writing on Megas- 
colex ceruleus, but, considering the large number of genera 
known, our information on the subject is still very scanty. If 
the anatomical relations of their afferent and efferent vessels 
be taken into account, we may conveniently distinguish two 
sets of capillary “ networks ” and term them respectively peri- 
pheral and intestinal networks. To the former category belong 
all capillaries in the body-wall, septa, nerve-cord, nephridia, 
and, indeed, all the viscera except the intestine. To the latter 
category belong the capillaries in the intestinal wall; and here 
we must distinguish in some worms between those in the 
anterior region and those in the region behind the gizzard, 
those in the anterior region having in some worms relations 
similar to those of peripheral networks, 
It is, I think, desirable to use the terms artery and vein for 
the vessels which have relations with the capillary networks, 
We can recognise : 
1. Arteries which carry blood from the main trunks towards 
capillary networks ; these arise from the main trunks and then 
repeatedly subdivide. 
2. Veins which carry blood from capillary networks to main 
trunks; these are formed by the repeated junction of smaller 
vessels, and finally open as single large vessels into a main 
trunk. 
3. Veins which, like the vertebrate portal vein, carry blood 
from one capillary network to another. These are vessels or 
