Minis have a doubling time of 2.4 days, maxis of 8 days. Minis regenerate head and foot 5 h faster than maxis. Minis have fewer tentacles (4.6) per head than maxis (6.1). In mini the concentration of the head activator is equal to that in Hydraattenuata, but the concentration of the head inhibitor is reduced (2-fold in the head, 1.2-fold in the body). The concentrations of the foot factors are normal. Minis respond like Hydra attenuata to head activator, foot activator and foot inhibitor, but they are less sensitive to head inhibitor In maxi the concentration of the head activator is higher than in mini (5-fold in the head, 10-fold in the body) and that of the head inhibitor is also higher (4-fold in the head, 5-fold in the body). The concentration of the foot inhibitor is normal, that of the foot activator is doubled. Maxis are insensitive to added head activator and less sensitive to added head inhibitor and foot inhibitor. Their response to foot activator is normal.