REGENERATION IN HYDRA ATTENUATA 



567 



viridissima Pall. With Kanajew (1926), Brien (1953), and others he emphasizes 

 the importance of thèse cells in hydroid régénération and tissue repair. 



Variously a synthesis of two or ail of the referents has been offered. Tardent 

 (1960) suggests that Goetsch's two régénération gradients be referred to " a single 

 quantitative principle " and that, as in tubularia a " distal dominant center may 

 well inhibit régénérâtes of another organ ". (Tardent, 1960, p. 39). He further 

 points to the coincidence of the morphological and metabolic gradients with the 

 interstitial cell distribution. 



Enlarging upon the notion of an inhibitor, Burnett (1960, 1961a and 1961b) 

 has proposed that régions of high metabolism exude a growth inhibiting factor 

 (as well as a growth stimulating factor), which prevents the formation of another 

 hydranth in its immédiate vicinity. The maintenance of hydra's form and the site 

 of the budding région are attributed to thèse two factors. 



Since a régénération gradient has not been clearly established, the first section 

 of this paper offers data toward an empirical définition of that term for Hydra 

 attenuata. 



The second section is concerned with the relation between budding and 

 régénération. Goetsch (1929), Lenhoff (1954) and Burnett (1961) have found 

 that régénération in budding animais is interfered with. Both Burnett and Lenhoff 

 term this interférence " inhibition ". Burnett (1961b) postulâtes an inhibitory 

 substance diffusing from the bud which prevents hydranth régénération until the 

 bud is separated from its parent. This idea results in certain implications regarding 

 the régénération performance of a budding animal which will be discussed here. 



The third section deals with feeding and régénération. Aside from scattered 

 statements by Koelitz (1911), Goetsch (1929), Eakin (1961) and others saying 

 that the régénération rate decreases with deprivation, little is known of the effect 

 of food quantity on the régénération performance. 



Finally, experiments concerning the effect of Actinomycin C and RNase on 

 regenerating halves of hydra are given with a view to obtaining initial information 

 concerning the rôle of RNA in hydranth and basai plate régénération. 



II. MATERIALS AND METHODS 



(a) Expérimental Procédures 



Ail experiments were carried out on animais from laboratory clones of 

 Hydra attenuata Pall. cultured since 1962 (Tardent, 1966). The clones were kept 

 at room température (21°C. — 23°C.) in Stendor dishes containing well water 

 and fed two to three pipets of plankton daily. Water was changed prior to each 

 feeding. 



