322 



THE BIOLOGY OF HYDRA : 1961 



A similar sequence of events was also observed in colonies reared 

 at 20° and at 19-23 : At 20° {± 1°) (Fig. 5) the frequency of all 

 three types of budding was reduced though the same basic bud- 

 ding pattern was observed: an obvious initial peak of hydranth 

 production, a phase of rapid frustule production followed by a slight 

 decline, and a phase of medusa budding. At 19-23' (Fig. 6) all 

 three types of budding were increased and the three phases of 

 asexual reproduction were again clearly demonstrated. 



Colonies grown at different temperatures clearly demonstrate 

 that under the relatively constant laboratory culture conditions three 

 expressions of morphogenesis occur in a sequence of distinct 

 phases. These activities are not mutually exclusive, but seem to ex- 

 hibit a clear separation between the different phases. The com- 

 mon basic pattern was observed at all temperatures, though certain 

 specific variations were noted in the duration of each phase as well 



201 IC 



1.0- 

 0.5 







4.5 



3.0 



1.5 







0.4 



0.2 

 



_i 1- 



-O O' 



Hydranths 



Fr ustules 



Medusae 



3 4 



10 II 12 



Fig. 5. Budding pattern of ten polyps reared at 20 (±1). Values on the 

 abscissa represent the number of buds of each type produced per colony. 



