EIPHT FIGURE6
A number of investigators, beginning with Friesen ('35, '36) have used x-rays to produce phenocopies. From the earlier experiments it had been supposed that high dosages (4000 r units and up) of x-rays applied to Drosophila larvae and prepupae killed all or almost all of the treated animals, since none of them hatched. However, Waddington ('42) found that even with dosages as high as 7000 r units, many flies continue development within the pupal cases up to the hatching stage but are unable to free themselves from the pupal integuments. By dissecting open the pupal cases, the flies may be examined. Waddington found some very curious developmental abnormalities resulting from the treatment, the particular type of abnormality depending primarily upon the time in development at which the radiation was applied.
The most interesting abnormalities were produced by radiations given to developing larvae between 60 and 90 hours after egg deposition and consisted of the overgrowth of parts and changes in histogenesis (e.g., formation of palps fronl eye material, of legs from antennae, or body surface material from wing epithelia). Some of this latter class of changes resembled certain of the homoeotic mutants (see Villee, '42a, for 'Aided by a grant from the Smith Research Fund of the Graduate School of Present address, Department of Biological Chemistry, Hnrvard Medical Rrhool. the University of North Carolina.