102 



POLYZOA. 



zoarium, and each individual of the colony as a polypide. 

 The entire skeleton is termed the ccenceciitm, and the 

 skeleton of each polypide a zoosdum. 



The polypide (fig. 27 A) has a sac-like form ; at the 

 upper end there is a platform or disc, the lophophore, on 

 which tentacles (t) are placed, arranged either in a circle 



\ 



FIG. 27. A, Diagram of the structure of a single polypide of a 

 Polyzoan. s, body-wall; t, tentacles; o, mouth; CBS, oasophagus ; 

 st, stomach ; int, intestine ; a, anus ; g, ganglion ; /, funiculus ; 

 ov, ovary ; sp, testis. B, Avicularium of Bugula, enlarged, b, beak ; 

 md, mandible ; C, chamber ; p, peduncle ; om, occlusor muscles ; 

 dm, divaricator muscles. (After Hincks, Brit. Mar. Polyz.) 



or in the form of a horse- shoe. The tentacles are not con- 

 tractile, but they are provided with cilia, which produce 

 a current of water that conveys food to the central 

 mouth (o). The anal aperture (a) is near the mouth, 

 generally below the lophophore, but in some forms within 



