In the course of testing the efficacy of roentgen rays in increasing somatic mutations (Cole arid Finley, '45) a considerable iiuniber of domestic pigcons of various ages were subjected to treatment. Others wei'e irradiated by Frisch ('44) in a study of feather growth. The two sets of esperiments were uniform in that in all cases the irradiation was 011 the right side only, the unirradiatecl left side serving as control. I n aclult bircls the right wing oiily was irradiated but in young squabs the wliole riglit side of the body was exposed, the left side being shielded liy lead plates. It soon became apparent that not only the rate of mutation aiicl of feather growth were affected by the r a y , but that in some cases skeletal growth also was iioticeably altered. It seemed possible that a detailed study of the cliaracter of the growth retardation might throw some light on the nature of the action of the rays on the growing tissues; consequently tlie wing holies were saved from both right and left wings of birds wliicli died or were killed as adultsin all but two cases more tlian 1 year of age. There were available for study the bones from: Group I. Group TI. Group 111.
25 birds treated at 1 to 15 days of age (after hatching) ; 10 birds treated at 5 nionths, 10 days to 9 years, 24 months of age; 8 hirds gireii no treatineiit, 1 month, 7 days to 3 years, 10 months of age.