1. Turtox Service Leaflet 39
2. BRIEN, P, BULLETIN DE LA SOCIETE ZOOLOGIQUE DE FRANCE 76: 277 (1951).
3. EWER, R.F., THE BEHAVIOUR OF HYDRA IN RESPONSE TO GRAVITY, PROCEEDINGS OF THE ZOOLOGICAL SOCIETY OF LONDON 117: 207 (1947).
4. American Museum Novitates 1949 1423
5. HYMAN, L. H., TRANSACTIONS OF THE AMERICAN MICROSCOPICAL SOCIETY 49: 322 (1930).