REGENERATION IN HYDRA ATTENUATA 



591 



visibly identifiable and this accumulation of pigment is designated by him as a 

 " Stage " bud. He further states that early buds (from State 1 onward) are more 

 effective in ,inhibiting' régénération than older buds. (This may, however, be 

 interpreted in terms of a graduai return to a non-budding, i.e., a regeneration- 

 responsive, condition). 



In any case, as far as questions of feeding and régénération are concerned, no 

 définitive statements can be made on the basis of the above experiments, both 

 environmental and physiological variables requiring more complète control. 



VI. THE EFFECT OF ACTINOMYCIN C AND RNASE ON 

 BASAL PLATE AND HYDRANTH REGENERATION 



(a) Introduction 



The effect of Actinomycin D and RNase on régénération in Stentor coeruleus 

 has recently been investigated by Whitson (1965) who found that both preexisting 

 RNA and newly synthesized RNA were necessary for the régénération of the oral 

 cone. Brachet, et al. (1964) have shown that Actinomycin D inhibits régénération 

 of nucleated halves of Acetabularia mediterrania more readily than anucleated 

 halves, indicating, according to the authors, that either messenger RNA has a 

 very long life or that it can be synthesized by the algae's cytoplasm. 



The effects of Actinomycin C (Bayer) and RNase on hydranth and basai plate 

 régénération in Hydra attenuata Pall. will be discussed here. Although the effects 

 of actinomycin on cell mechanisms are not yet completely known, it is at least 

 generally accepted that the synthèses of ail DNA-dependent RNAs are blocked 

 (Ingram, 1965). The experiments were performed with Actinomycin C (Bayer) 

 which is analogus to Actinomycin D (Merck, Sharp, and Dohme) (Zâhner (1965), 

 Cleffman (1965), Runnstrôm (personal communication to Tardent)). In any case, 

 by subjecting regenerating halves of hydra to actionomycin at various times after 

 the onset of régénération, it is possible to détermine the proportion of régénération 

 time, in each of the two halves, during which the processes blocked by actinomycin 

 occur. (Again, hydranth régénération time refers to the time taken for the first 

 appearance of a tentacle ; while basai plate régénération time means the time taken 

 to complète the basai plate). Similarly, a differential effect of RNase on distal and 

 proximal regenerating pièces might point to quantitative différences in the présence 

 and/or synthesis and/or dégradation and/or requirements of RNA in the two pièces. 



(b) Material and Methods 



Standard animais, as defined in Section II above, were used for ail experiments. 

 In any given experiment, no more than five halves were placed together in a small 



