FRESH-WATER POLYZOA. 235 



to form the stems, are opaque and black. The first or 

 foundation segment of the growth is larger than the 

 others, and its base expands into a broad disk, which 

 adheres to the stone and supports the entire stem. 

 Through the centre 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 flexibility which it has. 



The two segments near the free end of the stem are 

 smaller 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 contain the living animal, 

 the urns forming the stem below 

 them being filled with a soft, trans- 

 lucent, granular substance packed 

 into the cavity around the central 

 cord. 



The animal that produces this 

 beautiful series of brown urns 



Fig. 153. Urnat611a. 



lives at the free end of the pile 



solitary and alone with the exception of the temporary 

 companionship of those short branches which sprout out 

 near it, as shown in Fig. 158. It is these short growths 

 that are supposed to drop off and leave the cup-shaped 

 11* 



