FRESH-WATER POLYZOA. 



245 



PectinaUlla is not sensitive to sound, but a jar or a 

 shock to the water sends the animals into their con- 

 tracted state with surprising suddenness. The col- 

 onies are numerous throughout the summer and until 

 October, being most frequently found in the shade, 

 although they may live.in the sun if below the water. 

 Exposure to air and sunlight together is speedily 

 fatal. Therefore transfer the jelly to the collecting- 

 bottle as soon as possible, otherwise you will have, on 

 your return home, nothing but 

 a softening, slimy mass that 

 will soon force you to throw 

 it away. If suspended in a 

 large vessel of water kept 

 fresh by frequent change, 

 Pectinatella will live for some 

 time in captivity. In Fig. 169 

 (after Hyatt) is shown a small 

 colony with the lophophores 

 and tentacles expanded and 



enlarged, as they appear with a good pocket-lens. 

 The absence of color and motion, however, makes a 

 great difference in their beauty. 



In old colonies, especially late in the season, there 

 are often to be seen many small, rounded, brown 

 bodies, which as the animals die, float to the surface 

 of the water. These are the winter eggs or statoblasts. 

 They are formed within the body, and escape only 

 after the Polyzoon dies and melts, away, when they 

 float out and remain unchanged until the >varmth of 

 spring develops them. 



Under the microscope the statoblasts of Pectinatella 

 are seen to be encircled by a row of double hooks, as 





Fig. 169. — Pectinatella mag- 

 - nlfica. 



