Dissociability of developmental processes in the morphogenesis of the ear in Ambystoma, as revealed by X‐ray damage

Abstract

Eggs of Ambystoma maculatum from the same clutch were separated at Harrison's stage eight into three groups and maintained at So, 14" and 2OoC, respectively, until stage 28. At these three temperatures the respective number of hours between stages eight and 28 were 291, 171, 99. Half of each group was then x-irradiated with 600 r and the right ear vesicle substituted for that of the non-irradiated complement. Subsequent development of the irradiated grafts, a l l reared at 20"C, was compared among the groups. Within the range of temperatures employed, hypothermia alone has no effect upon final ear development; every left ear in all groups developed normally. Developmentl of irradiated grafts in the 8" group is decidedly more abnormal than in either 1 4 ' or The data demonstrate that the chronologically older ear is more radiosensitive t h a n the younger, despite morphological panty among groups at time of irradiation. This suggests that prolonged hypothermia may dissociate in time the invisible or biochemical processes of development from the purely morphological; the pace of the former is less retarded than the latter.