A PHENOMENON OF COMPETITION BETWEEN THE ANLAGE OF TIBIA AND FIBULA IN THE CHICK EMBRYO DEMONSTRATED BY X IRRADIATION

Leg buds of chick embryos at Hamburger-Hamilton stages of 18-21 were irradiated by total homogeneous radiation, selective radiation applied to the anlage of tibia or fibula, or total heterogeneous radiation. Total homogeneous radiation showed the respective potencies of the anlagen of tibia and fibula and revealed competition between them, as seen by normal differentiation of tibia and deficient development or absence of fibula. Selective irradiation of either anlage suppressed the competitive effect; the protected anlage developed normally. Selective irradiation of fibula anlage prevented its development but irradiation of tibia merely reduced tibial length. Total heterogeneous irradiation of leg bud restored the competition when the tibia received 3 times more radiation than fibula anlage, although the dosage received by fibula anlage was not sufficient to prevent fibula development. The results indicate that in radiationdamaged leg bud, surviving embryonic material is preferentially utilized for tibial development at the expense of fibular development. (H.H.D.)