VASCULAR SYSTEM OF PHERETIMA 361 
place with the other blood-vessels on the walls of the coeca 
themselves. 
An equally well-developed vessel runs along the mid-dorsal 
line of the gut, being only a specialized capillary of the internal 
plexus and being also continuous with the typhlosolar vessel 
behind. 
The external blood-plexus is almost completely absent in 
this region. ‘There are, however, a few capillaries present, 
which can be seen attached to the outside of the gut; for 
example, at places where the ventro-intestinal and septo- 
intestinal vessels join the wall of the intestine. But they soon 
enter the intestinal wall and pour their blood into the internal 
blood-plexus ; so that a regular external plexus such as we find 
in the second and third regions (vide infra) is absent in this 
part of the gut, the internal plexus being very strongly developed. 
(2) The alimentary plexus in the second region (twenty-sixth 
segment to twenty-three to twenty-eight segments in front 
of the anus). 
In this region we have both the external and internal plexuses 
well developed. The external plexus consists of capillaries of 
various sizes which are continuous on the ventral wall of the 
gut but not on the dorsal. They are connected with the septo- 
intestinals and the ventro-intestinals which apparently form 
their source of blood-supply. They open into the capillaries 
of the internal plexus as shown in fig. 2. 
The internal plexus in this region of the gut presents a very 
regular geometrical arrangement, as shown in fig. 3. This 
network consists of (a) Longitudinal capillaries, which 
are very closely set around the wall of the gut, extending all 
along its length. They are continuous from segment to seg- 
ment and number about forty all round. ‘These capillaries 
form the main portion of the plexus and in transverse sections 
are seen to lie in the folds of internal gut-epithelium. 
(b) Transverse Channels.—We have already men- 
tioned that in each segment the dorsal vessel is connected with 
the gut by means of two pairs of dorso-intestinal vessels. 
These dorso-intestinals on leaving the dorsal vessel enter the 
