POLEVZOA 181 
body-cavities of the various members of the colony are in free 
communication. 
The lophophore is in the form of a double horse-shoe, it 
bears from forty to fifty ciliated tentacles, which, by the current 
they set up, assist in bringing minute algae, etc., as food to the 
mouth. The bases of the tentacles are connected together by 
a fine membrane or web, sometimes called the calyx. On the 
side of the horse-shoe nearest the mouth is situated a ciliated 
extension of the body-wall. This lobe, which more or less 
overhangs the mouth, is the epistome. 
The alimentary canal is U-shaped, the mouth opens into 
an oesophagus, which is ciliated in some species. This leads 
into a stomach. From the stomach a rectum turns forward 
again and opens to the exterior outside the ring of tentacles, 
but not very far from their base. The walls of the intestine 
contain muscle fibres; the single layer of cells lining the 
stomach enclose brown granules, which apparently increase 
in number with the age of the polypide. These are probably 
excreta, which for some reason or another do not find their 
way out of the body. 
A strand of tissue of considerable importance in the life- 
history of the animal passes from the posterior end of the 
stomach, and is attached to the body-wall of the animal, near 
the posterior end. It is termed the fwniculus, and doubtless 
serves to prevent the polypide from being extruded too far. 
The coelom is spacious, and contains a corpusculated fluid which 
is kept in motion by the ciliated cells lining the body-wall. 
It is continued into the lophophore, and into each tentacle, but 
is partly divided into two by an incomplete septum which 
stretches across the body below the level of the base of the 
lophophore. 
The nervous system consists of a bilobed ganglion lying on 
the oesophagus, between it and the anus. It is situated just 
in front of the imperfect septum which stretches across the 
animal in this region. At the sides the two lobes extend 
round the oesophagus, forming a complete circum-oesophageal 
nerve ring, each lobe also gives off a nerve which runs along 
the base of the lophophore, and which furnishes a small nerve 
to each tentacle. 
