MOSS-POLYPES 



437 



IS 



the homes of the constituent zooids. Another common form 

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

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



Fig. 269.— Polyzoa. r, Sea-Mat {Flusira); a, Sea-Net {Retepordi 



The structure of the group is most conveniently studied in 

 one of the fresh-water Polyzoa, the Pliime Coralline {Plumatella 

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



Fig. 270. — Polyzoa, enlarged 



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

 others in different states of retraction, u. Diagram of a sbgle 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 



