ANATOMY OF THE EARTHWORM. 109 
hypothesis sometimes hazarded as to the function of the water- 
vascular system of Scolecida or the blood-sinuses of Arthro- 
pods. There can be no doubt that the vascular system of the 
earthworm, as in other Annelids, is adapted for exposing its 
fluid to the action of oxygen. How does it do this, and has 
it any other functions? In no Annelid can it be satisfactorily 
shown that the vascular fluid has a definite circulation ; the 
fluid is made to move, to oscillate, and pass more or less from 
one series of vessels to another by the contractions of the 
vessels, but, as M. Milne Edwards observes, there is no definite 
circle of movement. In certain Annelids M. De Quatrefages 
has shown that the perivisceral fluid absorbs oxygen ; this he 
has demonstrated chemically, and it appears that, as a rule, 
the perivisceral fluid absorbs oxygen, to which the vessels of 
the vascular system afterwards become submitted. In the 
earthworm, then, it is probable that the perivisceral fiuid 
absorbs oxygen or water containing oxygen through the 
capillary canals forming a characteristic structure of the 
integuments. To the action of this the fluid contained by the 
vascular plexuses and the great vessels is everywhere more or 
less exposed by osmotic action. It would appear also that 
this process takes place to a very large extent in the vessels 
distributed to the numerous diaphragmatic muscles, which are 
necessarily very largely subject to the action of the perivis- 
ceral fluid. 
Another vastly important function of the vascular fiuid, 
and one for which it seems specially adapted, is excretion. 
This takes place through the segment-organs, and is also 
shared in a minor degree by the perivisceral fluid which is 
continually passing through them. 
Absortion of alimentary matters may equally be the func- 
tion of both fluids; certain matters passing by osmoseS 
through the very delicate walls of the intestine into the peri- 
visceral cavity, and others possibly, though not very pro- 
bably, being absorbed by the delicate networks formed by 
the visceral branches of the vascular system. It has been 
hinted by Claparéde* that the greenish-yellow mass of 
granules enveloping the intestine and the dorsal vessel and 
its branches, even at its anterior extension, may have some 
connection with the formation of the corpuscles of the peri- 
visceral fluid, and assist materially in other respects in 
the functions of that liquid. It appears very certain that 
in the earthworm the perivisceral fluid absorbs aliment 
through the intestinal walls, and nourishes all the organs 
which it bathes, and also it brings oxygen to the vascular 
* © Recherches sur les Oligochetes.’ 
