406 



THE BIOLOGY OF HYDRA : 1961 



TABLE 3 



Effect of temperature on regeneration 



Tentacle Numbers at 48 hours 



Each value represents the average of 18 replicates. 



"Maintenance temperature of stock clones; temperature during period of regeneration 

 was 27° for both groups. 



peiature (27^) used during the established regeneration testing 

 procedure, a phenomenon subsequently shown to be related to differ- 

 ences in the interstitial cell patterns of the organisms maintained 

 at the two temperatures. 



The effects of nutrition on regeneration rate were pointed out 

 by Ham (1) who found that even the elimination of one feeding 

 has an adverse effect upon the regeneration rate for a few days 

 thereafter. A more detailed study of this effect showed that: (a) 

 one day's fasting markedly lowered the regenerative capacity of 

 the organisms that were cut in the mid-stomach region, the regen- 

 erative ability being lowered, in fact, just as much by a 24 hour 

 fast as is observed after three and five day periods of fasting; 

 (b) but the regenerative ability of those cut just behind the hypo- 

 stome was not significantly aftected until the hydra had been 

 starved for three or more days. 



In studying depressed organisms, it was found that some "slight- 

 ly depressed" and "moderately depressed" hydra are capable of 

 regenerating as fast as, or faster than, the control hydra at 18 

 hours, and some are able to regenerate as many tentacles. Although 

 not all the "depressed" and "slightly depressed" hydra regenerate 

 as well as the controls, the fact that some are capable of doing 

 so would indicate that depression in itself does not interfere signi- 

 ficantly with the regeneration rate. Only severely depressed hydra 

 are unable to regenerate. These hydra, however, are unable to 

 eat so that their regenerative ability may be impaired according to 



