378 HISTORY OF BBITISH ZOOPHYTES. 



gizzard. They are very vigorous in their movements. It 

 is very interesting to watch the little creatures manceuvring 

 their cells. Every now and then, as if some common 

 impulse stirred them, all the polypes on a single pinna 

 will move forward their cells, and the frond close like the 

 Mimosa-\eh( when touched. More commonly they are in- 

 dependent in their movements. A single cell here and 

 there will be seen in motion, while the rest remain quiet. 



"The mouth of the cell is furnished with the charac- 

 teristic setse of the family. When the cells are detached, 

 the circular opening near the base may easily be detected." 

 {Hinch.) 



11. POLYZOA HYPPOCREPIA. 



The following is Professor Allman's arrangement of the 



genera :- 



Polype-mass floating. CRisTATELLiDiE. 



One genus only — Ceistatella. 

 Polype-mass rooted. 



t Massive or confervoid, inarticulate. PLUMATELLiDiE. 



Massive and sponge-Kke. Alcyonella. 



Confervoid, tentacular disc crescentic. Plumatella. 



