DISSOCIABILITY OF DEVELOPMENTAL PROCESSES IN MORPHOGENESIS OF EAR IN AMBYSTOMA AS REVEALED BY X-RAY DAMAGE

Eggs of Ambystoma maculatum from the same clutch were separated at Harrison's stage eight into three groups and maintained at 8°, 14° and 20°C, 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, all 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. Development of irradiated grafts in the 8° group is decidedly more abnormal than in either 14° or 20° groups. With the exception of the VIIIth ganglion, development of the grafts in 14° and 20° groups is approximately the same. On the basis of 8° = 1, average developmental ratings for the three groups are approximately as follows: size — 1:2:2. differentiation — 1:2:2. ganglion — 1:2:5. The data demonstrate that the chronologically older ear is more radiosensitive than the younger, despite morphological parity 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. Copyright © 1968 Wiley‐Liss, Inc.