1. Burnett, A. L.: The acquisition, maintenance and lability of the differentiated state in hydra. In: The stability of the differentiated state (H. Ursprung and W. Beermann, ed.). Berlin-Heidelberg-New York: Springer 1966.
2. Campbell, R. D.: Tissue dynamics of steady state growth inHydra littoralis. Develop. Biol.15, 487?502 (1967).
3. David, C. N.: Quantitative method for maceration of hydra tissue. Wilhelm Roux' Archiv,171, 259 (1972).
4. Kanaev, J. J.: Hydra. Essays on the biology of fresh water polyps, originally published by Soviet Academy of Sciences, Moscow; ed. by H. M. Lenhoff (1952).
5. Lentz, T. L.: The cell biology of hydra. Amsterdam: North-Holland Publ. Co. 1966.