FRESH -WATER POLYZOA. 233 



joint or cell being club-shaped. The colonies are irreg- 

 ularly branched, and are built up of a single row of cells 

 placed end to end, the 

 narrow end or the handle 

 of the club being attached 

 to the broad end of the 

 cell immediately behind 

 it. The opening through 

 which the animal pro- 

 trudes its Circular lo- Fig. W.-Palndicella. 



phophore is at one side 



of the broad end of each cell 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. 



6. URNATELLA (Fig. 158). 



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 con- 

 spicuous objects to the eye of a microscopist, Urnatella, 

 must be especially searched for. The colonies, or stem- 

 like growths which it forms, are composed of urn-shaped 

 cells or segments united end to end, and attached by a 

 single disk-like enlargement to the supporting object 

 from which they hang suspended. The lower surface 

 of stones, beneath which the water constantly flows, 

 seems to be Urnatella's favorite haunt. The stem-like 

 colonies of urns are usually found two together pendent 

 from the same disk of attachment, and appearing some- 



