RADIATION AND THE STUDY OF MUTATION IN ANIMALS 1231 



cells of different types to a given dosage of radiation. These experiments 

 have all been done with Drosophila melanog aster; only exploratory data 

 are available in Habrobracon (Whiting and Bostian, 189). 



If a male Drosophila is irradiated and mated at intervals to a succes- 

 sion of virgin females, the progeny from the different broods will have 

 Table 10. — Age of Germ Cells and Lethal-mutation Rate in the 



X-CHROMOSOME OF DrOSOPHILA MELANOGASTER 



Data of Harris (72): X-ray treatment of adult cf cf; tungsten target, 50 kv. 10 ma., 



13 cm., 30 min. 



Data of Hanson and Heys (62)-. A. cf cf treated with 150 mg. Ra for 9 hr. ; S. cf cf 



treated with X-rays "circa ^i ra dose" 



Age of germ 



cells in days after 



X-raying 



1-7 



7-14 



14-21 



21-28 



28-35 



A 



Percentage 



of lethals 



13.00 



14.20 



1.01 



4 30 



0.00 



B 



Number of 



tested 



chromosomes 



504 

 605 

 614 

 470 



Percentage 

 of lethals 



6.5 

 6.4 

 2.9 

 2.1 



Data of Timofeeff-Ressovsky (178): males irradiated once with 2500 r; mated to 



virgin 9 9 every 5 days 



