MOSS-POLYPES 



437 



the homes of the constituent zooids. Another common form is 

 the Lace-Coralline (Membranipora), seen at low tide as a delicate 

 lace-like encrustation upon the large brown sea-weeds. 



Fig. 269. Polyzoa. i, Sea-Mat (Flustra}; 2, Sea-Net (Retepord) 



The structure of the group is most conveniently studied in 

 one of the fresh-water Polyzoa, the Plume Coralline (Plumatella 

 repens] (fig. 270), the branched creeping colonies of which are 



A. 



CHETORY 

 OPENING 

 NGLION. 



Fig. 270. Polyzoa, enlarged 



A, Small colony of Lophopus crystallinus, showing some individuals fully extended, and 

 others in different states of retraction. B, Diagram of a single individual of Plumatella, cut 

 through centre of body. 



found creeping upon stones and other objects. The skeleton is 

 horny, and from the tip of each branch a zooid can be protruded, 

 the free end bearing the mouth surrounded by a double crown 



