POLYZOA. 307 



convolution below ; and returns again, terminating in an excretory 

 orifice under the base of the tentacula." 



The inhabitants of the colony are thus united in great numbers 

 under one common envelope ; a peculiar downy appearance is pro- 

 duced by the collection of tentacula belonging to this curious colony. 

 The filamentous looking mass is the translucent row of cells in which 



fjUJ '.>vno^:n 

 Fig. 122. Flustra foliacea (Linnaeus). 



the polyps are lodged, and to which they retreat when disturbed. 

 These cells are sometimes free in part, sometimes completely rooted 

 to the stems of aquatic plants. The tentacles are of a fine transparent 

 glass colour, the body being of a brown colour. Fig. 121 represents 

 Cristatella mucedo, which is not uncommon both in this country and 

 in France. 



Most naturalists have now agreed to place among the Polyzoa 



