POLYZOA 



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 mmiber 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 funiculus, 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. 



