SECT. rx. POLYZOA, 219 



in the surrounding water an ascending stream on the 

 outside, and a descending one on the inside. When any 

 particles of food that may be carried down the inner 

 surface of the tentacles arrive at the mouth, a selection 

 is made, the rejected particles being carried off by the 

 stream, while those that are chosen are received by the 

 funnel-shaped mouth, and pass through a valve in the 

 gullet into the stomach, where they are kept in con- 

 tinual motion by cilia, and the refuse is ejected by an 

 orifice near the mouth. 



\ 



Fig. 158. Cells of Lepralise. A, L. Hyndmanni ; B, L. fignlaris ; c, L. verrucoea. 



Fig. 158 represents the cells of different species of the 

 genus Lepralia, which form crusts upon marine objects. 

 Other genera grow as independent plant-like structures, 

 and some take an arborescent form, and creep over rocks 

 and stones. The Cellularia ciliata, of which fig. 159 is 

 a magnified portion, rises in upright branching groups 

 like little shrubs ; and as many are commonly assembled 

 together, they form miniature groves, fringing the sides 

 of dark rocky sea pools on our coasts. Most of the 



