1002 Noture and schema aspect ot fixation Histologic aspect Cephatic region Trunk region Totat X-irradiation Control of operation Mocroscopic animal pole Irradiation of @,O|O (LL protective Irradiation of vegetative pole screen 4 aes Rnnceaernn racaracacsrerereecereete et SENSEREE eee ee eerereTE see 68888833888 % OF STRUCTURES INDUCED Fig. 1—Result of irradiation with 1170 R on the young Pleurodcle gastruia. T2 NORMAL 1170 R 30,000 R 150,000 R Fig. 2— Percentage of structure induced in a fragment of ectoderm by a dorsal blastoporal lip, either normal or X-rayed.