566 GABRIELE KASS-SIMON 



V. FEEDING AND REGENERATION 586 



(a) Introduction 586 



(b) Materials and Methods 587 



(c) Results 587 



(d) Discussion 590 



VI. The Effect of Actinomycin C and RNase on Basal Plate and Hydranth 



REGENERATION 591 



(a) Introduction 591 



(b) Material and Methods 591 



(c) Results 592 



(d) Discussion 595 



VII. General Discussion 596 



Summary 596 



Résumé 597 



Zusammenfassung 597 



Bibliography 598 



ACKNOWLEDGEMENT 



I wish to thank Professor Pierre Tardent for his advice and good counsel. 

 I also wish to thank Mr. Hans-Ruedi Wildermuth for executing the diagrams. 



I. GENERAL INTRODUCTION 



Hydra's morphological polarity has led to a number of théories concerning 

 biological gradients in the animal. The term , gradient' has taken on a number of 

 meanings and been variously defined. Goetsch (1925, 1929), Burt (1925, 1934), 

 Tardent (1954, 1960), Burnett (1960, 1961) have used the term with respect to 

 the ability or tendency of a given axial région to regenerate either a hydranth or a 

 basal plate. Burt (1934) gives some expérimental évidence for such a gradient and 

 depicts two complementary linear gradients for basal plate and hydranth régénéra- 

 tion, (ibid. p. 81) 



Child (1941, 1947, 1948) and his followers (Child and Hyman, 1919) speak 

 of metabolic gradients on the basis of experiments demonstrating axial différences 

 in susceptibility to certain toxins. 



A third meaning for the term is given by Tardent (1952) who has demonstra- 

 ted a steady axial décline in the number of interstitial cells along the axis of Hydra 



