FRESH-WATER POLYZOA. 231 



roundings were not quite favorable, perhaps the proper 

 food was not attainable, so they died. 



2. CRISTATELLA. 



The form and movements of Cristatella have already 

 been referred to on page 225. The young colonies are 

 rounded, and are found in the same localities with Pec- 

 tinatella. The statoblasts are circular and have two 

 rows of double hooks, one row around the border, the 

 other nearer the centre. In both, the hooks are not sim- 

 ple as in Pectinatella, but have several branches at the 

 top of the stern, and the tips are forked. 



According to the writer's experience, Cristatella is not 

 common. 



3. PLUMATELLA (Fig. 156). 



The tubes containing the animals may be attached 

 only at the base, or the whole colony may be adherent 

 to the submerged surface on which it grows. It is to 

 be found in shallow water, 

 usually near the shore. To 

 see the lophophore and ex- 

 panded tentacles, if the col- 

 ony is small, it may be re- 

 moved by slicing the wood 

 to which it is attached, the 



Fig. 156.-Humatella. 



slice to be placed in a watch- 

 glass of water on the microscope stage, which must, of 

 course, be in a horizontal position. The mirror may 

 then be swung above the stage, and Phimatella viewed 



