FRESH-WATER POLYZOA. 



249 



horseshoe-shaped. The colonies are usually small, 

 covering a snaall space. The tentacles are nevermore 

 than twenty-four in number. The statoblasts are 

 more or less ovate or reniform, and are without spines 

 or hooks (Fig. 173). 



6. Paludic^lla (Fig. 171). 



These colonies may always be distinguished from all 

 other tube-making Polyzoa by their jointed appear- 

 ance, each joint or cell 

 being club-shaped. 

 The colonies are ir- 

 regularly branched, 

 and are built up of a 

 single row of cells 

 placed end to end, the 

 narrow end, or the 

 handle of the club, be- 

 ing attached to the 

 broad end of the cell 

 immediately behind it. 



The opening through which the animal protrudes its 

 circular lophophore is at one side of the broad end of 

 each cell and near the top. The base alone may be 

 attached, or the stem may be adherent and some of 

 the branches free, as in the figure. 



7. Urnatella (Fig. 172). 



The form and appearance of this Polyzoon are so 

 characteristic that it need never be mistaken; but 

 while the other members of the group are usually 

 rather conspicuous to the eye of a microscopist, 

 Urnatella gracilis must be especially searched for. The 



* Fig. 171. — Paludic^lla. 



