POLYZOA. 



243 



POEID^, has the colony lamellar and irregular, incrusting the surfaces of sub-marine 

 objects, or upright and branching. In Cellepora an avicularium exists in the median 

 line, just behind the posterior margin 

 of the mouth of the cell, -while in Cel- 

 leporaria it is absent. The Retepoe- 

 iD^ are graceful forms, in which the 

 cells unite to form a flat, leaf-like col- 

 ony, which is perforated with numer- 

 ous oval openings. 



Order II. — PHYLACTOL^- 

 MATA. 



This order embraces the fresh-water 

 Polyzoa proper, none of its members 

 being found in the sea. They have 

 the tentacles arranged on a horseshoe- 

 shaped lophophore, while the mouth may be closed by a tongue-shaped lid, known as 

 the epistome, which is placed just above the rudimentary brain. In size these forms 



Fig. 244, — Myrktzoum subgracile. 



Fig. 245. — Metepora celluloea. 



are much larger than their marine relatives, while their general appearance is much 

 more uniform. They are found beneath stones in running brooks, attached to sub- 

 merged logs in lakes and ponds, and in the case of CristateUa the whole colony is free, 

 and has the power of motion as a ,whole. The number of species known, from the 



