252 AQUATIC MICROSCOPY FOR BEGINNERS. 



brown urns lives at the free end of the filament, soli- 

 tary and alone, with the exception of the temporary 

 companionship of those short branches which sprout 

 out near it, as shown in Fig. 172. It is these short 

 growths which are supposed to drop off and to leave 

 the cup-shaped scars on each side. Rarely are there 

 • more than two of these projecting scars on each urn. 



The animal itself, which terminates the main stem 

 and its branches, when in active condition, appears, 

 Dr. Joseph Leidy, its discoverer, says, as a bell-shaped 

 body with a widely expanded oval or nearly circular 

 mouth, directed obliquely to one side or ventrally. 

 The mouth of the bell is bordered by a broad waving 

 band or collar, from the inside of which springs a cir- 

 cle of tentacles. Of these there are usually sixteen, 

 though sometimes from twelve to fourteen. They are 

 invested with an epithelium furnished with moderately 

 long, active cilia.* 



Like most of these beautiful creatures, Urnatella is 

 exceedingly timid and sensitive. At the slightest dis- 

 turbance the tentacles are folded together and drawn 

 into the mouth of the bell, which closes around them, 

 and the entire stem suddenly bows' itself down to the 

 ground, or, when long, rolls itself into a loose coil. 



No eggs nor statoblasts have been observed. Dur- 

 ing the winter the urns do not seem to become sepa- 

 rated from one another. "Perhaps, as reproductive 

 bodies, after the polyp-bells perish, they remain in 

 conjunction securely anchored through the first of the 



* "Urnatella gracilis: A Fresh-water PolyzoOn." By Professor 

 Joseph Leidy. Journal of the Academy of Natural Sciences of Phil- 

 adelphia, vol. ix. 



