FRESH-WATER POLYZOA. 



251 



The central enlarged portion of the urns is translu- 

 cent, light-colored, and often with many transverse 

 wrinkles and transverse brown lines. It is also brown 

 spotted, and has many little tubercles of the same 

 color. The necks of the urns where they are joined 

 together to form the stems, are opaque and black. 



The first or foundation segment of the growth is 

 larger than the other members of the group, and its 

 base expands into a broad disk, which adheres to the 



stone and supports the entire 

 stem. Through the center of 

 the whole collection of urns 

 passes a cylindrical cord whose 

 purpose would seem to be to 

 strengthen the fragile pile, 

 and to give it the great flex- 

 ibility which it possesses. 



The two segments near the 

 free end of the stem are small- 

 er than the others and rather 

 different in shape. They are 

 also nearly transparent and 

 colorless. They seem to be 

 urns in the process of growth, 

 while those below are matured 

 and hardened. It is only the 

 terminal segments that con- 

 tain the living animal, the 

 urns which form the stem be- 

 low them being filled with a soft, translucent, granular 

 substance packed into the cavity around the central 

 cord. 



The animal that produces this beautiful series of 



Fig, 172. — Urnatella. 



