704 M. BORNER UND P. TARDENT 



2. Every sudden change from one light intensity to another modifies the séquence 

 of spontaneous contractions in a typical manner: A short period (6 min. 

 during which the polyp expands is followed by an accelerated séquence ol 

 contractions, lasting about 30 min. If the light intensity remains unchanged 

 this hyperactivity gradually returns to a basic fréquence of spontaneous 

 contractions. 



3. The influence of light upon the spontaneous activity of hydra is discussed. 



LITERATUR 



Haug, G. 1933. Die Lichtreaktionen der Hydren. Z. vergl. Physiol. 19: 246-303. 

 Passano, L. M. 1962. Neurophysiological study of the coordinating Systems and pace-\ 

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— und C. B. McCullough. 1962. The light response and the rhythmic potentials of 



Hydra. Proc. nat. Acad. Sci. Wash. 48: 1376—1382. 



— 1963. Pacemakers hiérarchies controlling the behaviour of hydras. Nature 199: 



1174—1175. 



— 1964. Co-ordinating Systems and behaviour in Hydra I. J. exp. Biol. 41 : 643 — 664. 



— 1965. Co-ordinating Systems and behaviour in Hydra IL J. exp. Biol. 42: 205 — 231. 

 Rushforth, N. B., A. L. Burnett und R. Maynard. 1963. Behaviour in Hydra: 



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Sollberger, A. 1965. Biological rhythm research. Elsevier Publ. Co., Amsterdam. 

 Tardent, P. 1966. Zur Sexualbiologie von Hydra attenuata Pall. Rev. Suisse Zool. 73: 

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— und E. Frei. 1969. Reaction pattems of dark-and-light adapted Hydra to light 



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