570 



GABRIELE KASS-SIMON 



regenerating one in a later period. In addition, since u is équivalent to 24 hours, 

 the handicap suffered by 25% and 10% levels in FTN and FTN-ITN évaluation 

 is to some extent mitigated. 



It is clear that thèse factors are merely measures of the régénération phenome- 

 non and in no way refer to possible physiological mechanisms not here investi- 

 gated. The data was subjected to one of the following statistical tests : " The analysis 

 of Variance " (F-Test), the " ,Students' t-test' " and the X 2 test (Henrysson, et al. 

 1960, Moroney, 1962; Wallis and Roberts, 1956) and the results are given in 

 ternis of F, t or X 2 , accordingly. Except in 2 experiments (see Sections IV & V), 

 each clone was treated as a separate population, since ail 4 clones were not of the 

 same sex and the effect of ,male' or ,femaleness' on régénération has not yet been 

 fully clarified. 



III. THE PROBLEM OF A REGENERATION GRADIENT 

 (a) Introduction 



The presumed régénération gradient has long been attributed to concomittant 

 gradients of one sort or another. It has been thought to resuit from a hierarchy of 

 structure wherein more distal parts manifest (a) a higher rate of metabolism 

 (Child, 1941, 1947, 1948; Weimer, 1932, 1934), (b) a greater number of interstitial 

 cells (Tardent, 1952, 1954), or (c) an inhibitor-producing structure (Burnett, 

 1961a, 1961b). 



Now the notion of a gradient supposed to effect régénération, regardless of 

 whether it is attributed to metabolic, cytologie or inhibitory dominance, implies 

 that along the axis of the hydra, any two adjacent régions stand in ranked relation 

 to one another with respect to the speed of hydranth and/or basai plate régénéra- 

 tion, if the décline in the gradient is steady. Further, the notion of a diffusing 

 substance solely responsible for an assumed régénération gradient as postulated 

 by Burnett (1960, 1961a, 1961b) and Tardent (1960) implies that, other things 

 being equal, and in the absence of the inhibitor-producing structure, ail axial levels 

 of hydra would have the same ability of regenerating that structure. 



In order to investigate thèse implications, the following experiments were 

 performed : 



First, the speeds of hydranth and basai plate régénération at various axial 

 levels were determined and are given below as the Time of Tentacle Differentiation 

 (TDT), and the Time of Basai Plate Differentiation (BDT). Secondly, the régénéra- 

 tion performance at the various axial levels was determined by a considération of 

 the final number of tentacles regenerated in a given period of time (FTN), by the 



