GEPHVREA 163 
cells. From the longitudinal bundles four stout muscles arise, 
two dorsal and two ventral. These pass to form a muscular 
ring ensheathing the oesophagus, just behind the head. They 
are termed the four vetractors, and their function is to draw 
in the introvert. 
The alimentary canal consists of a straight oesophagus, 
into which the mouth passes without any armature, and 
which in its turn passes into a coiled intestine. Both these 
parts are ciliated, the cilia of the oesophagus being continuous 
with those of the lower hp and tentacles. The intestine is 
coiled round a special “spindle” muscle, which arises from the 
extreme posterior end of the body, passes up the axis of the 
coil, and joins the longitudinal muscles of the body-wall near 
the anus (Fig. 104). A short rectum passes to the anus 
which terminates the alimentary canal, the anus pierces the 
body-wall just behind the line of division between the introvert 
and the trunk. 
The vascular system is closed and is confined to the anterior 
end of the animal. Its most conspicuous part is a vessel which 
lies on the dorsal side of the oesophagus between the retractor 
muscles. The vessel is closed behind, and gives off no capillaries. 
At the anterior end it opens into a large sinus into which the 
brain protrudes; from this sinus a circular vessel is given off 
which runs round the lower lip, and when full of blood, it 
serves to distend the latter. Another part of the vessel runs 
along the base of the lophophore, giving off branches into each 
tentacle. It is possible that the blood may become oxygenated 
in the tentacles, but the chief function of the whole system is 
to distend the tentacular crown and lower lip. The fluid in 
this system is corpusculated. 
The coelom is very spacious, and contains a corpusculated 
fluid which bathes all the internal organs. The corpuscles 
are larger than those of the vascular system. The contraction 
of the circular muscles of the skin forces this fluid forward, 
and in this way the introvert is everted. 
The nephridia, or excretory organs, of the Gephyrea are 
often termed “ brown tubes.” In Phymosoma they are two in 
number, one on each side of the ventral nerve cord (Fig. 104). 
They have the form of elongated sacs, which hang down 
