326 THE BIOLOGY OF HYDRA : 1961 



15 



■5 12 



I 9 - 2 3 C 



Fig. 8. Relationship of frustule budding and medusa budding at different 

 temperatures. Values on the abscissa represent the number of frustules 

 produced per colony per week. Arrows indicate the appearance of the first 

 medusa buds. 



maintained at 23" or below. Frustules from such cultures were gen- 

 erally opaque as a result of large reserves of food material contained 

 in the gastrodermal cells ( 16, 17 ) . These food reserves occurred 

 in distinct cytoplasmic granules or droplets and appear to be simi- 

 lar to the "protein reserve droplets ' or "spherules de reserves" con- 

 tained in the gastrodermis of Hydra oligactis (4), Hydra attenuata 

 (23), and in the polyp stage of the African freshwater medusa 

 Limnocnida (1). Histochernical tests have indicated that these 

 granules or "reserve bodies" may contain RNA, DNA, protein, car- 

 bohydrate, and fats in varying proportions. 



Frustules produced by Craspedacusta colonies cultured at 

 temperatures higher than 23° are appreciably less opaque, indi- 

 cating smaller amounts of reserve food materials. Colonies reared 

 from 27° frustules demonstrate a strikingly different developmental 

 pattern from those rean^d from frustules produced at low 

 temperatures. 



