274 THE MICROSCOPICAL NEWS. 
branches, called pertvzscerals, communicate between the two main 
vessels, either with or without the intervention of the cutaneous 
plexus. Some of the anterior perivisceral branches are much en- 
larged and pulsate, forcing the blood into the ventral vessel; they 
are therefore called hearts. 
It has been a question which of the two fluids (the perivisceral 
and corpusculated, or the vascular and non-corpusculated) repre- 
sents the true blood. Dr. Carpenter considers the corpusculated 
fluid to be the blood, which obtains aération from the fluid in the 
vascular system, the branches of which act as internal gills. Dr. | 
T. Williams and Dr. W. C. McIntosh, however, affirm, and it is 
now generally believed, that the coloured fluid, contained in the 
vascular system, is the true blood, and the corpusculated perivis- 
ceral fluid is chyl-aqueous in its character. Respiration is regarded 
as being accomplished by means of the cutaneous and intestinal 
plexuses of the vascular system, which are in contact with the 
water external to the body, and with that which flows through the 
alimentary canal. 
It is also believed that the perivisceral fluid has a mechanical 
use as an aid to locomotion. Dr. Thomas Williams, in his Report 
on British Annelids, published in the British Association Reports 
for 1851, says :—‘“In all annelids the swelling of certain portions 
of the body in progression is accomplished by aid of the fluids of 
the interior. This is driven to a given point of the containing 
cavity, and then momentarily imprisoned there by the contraction 
of the circular integumentary muscles in front of it and behind it. 
Hereat, for a moment, the body bulges, the muscles of the integu- 
ment are then excited to action, and the fluid is forcibly compressed 
forwards and backwards, according to the direction of the muscular 
AP ENCY sis)! % Nearly all annelids are struck with paralysis when 
this fluid is made to escape from its cavity by a puncture through 
the external walls. The power of voluntary motion is suspended. 
The body of the worm becomes passive and flaccid. The perito- 
neal (perivisceral) fluid is really the fulcrum on which all muscular 
action is based. Without it, the worm cannot direct the contraction 
of its muscles with efficiency and precision. But its mechanical 
uses are not exclusively limited to the aid afforded in progression. 
It prevents mutual and injurious pressure amid the internal organs, 
without which the course of the blood in its proper vessels is ar- 
rested ;” and “on it, as on a pivot, the vermicular motion of the 
intestinal cylinder is performed.” 
Internal septa divide the animal into numerous segments, and 
orifices in the septa allow the perivisceral fluid to pass from one 
segment to another. The alimentary canal, which passes through 
the septa, and is slightly constricted thereby at ‘each septum, is of 
a simple character, consisting only of a pharynx, cesophagus, and 
