REGENERATION IN HYDRA ATTENUATA 



595 



P < 0.01) while the drop in inhibited basai plate régénérâtes is not significant. 

 (Table 12, rows 8 and 9). When treatment is delayed for another two hours, while 

 the number of inhibited tentacle régénérâtes remains constant, there is a sudden 

 significant drop in the number of inhibited basai plate régénérâtes (Table 12, 

 rows 9 and 10, X 2 =9.5, P < 0.01). The drop between 12 and 17 hours is not 

 significant for either basai plate or tentacle régénération. With the exception of 

 animais treated 4-6 hours after transection (TDT=56.10 ± 20), tentacles and 

 basai plates regenerated at times comparable to standard animais. 



(d) Discussion 



Since treatment with actinomycin from the time of transection virtually 

 inhibits ail régénération, it is to be assumed that any pre-existing RNA will not 

 support either hydranth or basai plate régénération, as defined, the necessary 

 RNA's being synthesized after transection. In support of this, RNase pretreatment 

 alone does not inhibit régénération, but can cause a delay in the appearance of the 

 regenerate ; (although vérification of the actual effects of both RNase and actinomy- 

 cin in the animal are required). When RNase treatment is continuous and inhibition 

 less than 100%, a significantly greater number of distal halves are inhibited than 

 proximal halves. Although the question of whether this is due to slower synthesis, 

 by distal halves, or to greater requirements for the régénération of the alternative 

 structures, or to différences in already existing RNA quantities or to différences in 

 maintainance requirements with concomitant différences in dégradation speeds 

 cannot be answered at the level of this investigation, the differential response is 

 clear. 



Since animais treated with actinomycin, regardless of whether they represent 

 distal or proximal halves, die at comparable times, différences in the régénération 

 responses are probably not due to différences in the existing RNA quantities or 

 to différences in the speed of its dégradation, but to différences either in the rates 

 of synthesis during régénération of the alternative structures or to différences in 

 the minimum requirements for each of the structures to become manifest. This 

 last is further supported by the fact that with delayed actinomycin treatment, proxi- 

 mal halves reach the thresh-hold of almost total régénération earlier than do distal 

 halves. (For both, it will be noted, the time needed for the processes blocked by 

 actinomycin to occur represents approximately y$ of the respective régénération 

 times). 



Nonetheless, because the effects of actinomycin are not yet completely known 

 and because Basai Plate and Tentacle Differentiation Times are, to some extent, 

 artificial criteria, statements concerning the relative amounts of RNA either 

 synthesized or required during the régénération of basai plate and tentacles by 

 distal and proximal halves are left open for vérification at other levels. 



