146 H. K. MITCHELL AND J. R. SIMMONS 
ACKNOWLEDGEMENTS 
This work was supported in part by funds from the National Science Foundation 
(G-4859) and the United States Public Health Service (H-3103). Work on the Droso- 
phila mutants was done under the tenure of a National Science Foundation Senior 
Fellowship. For this, the senior author acknowledges with pleasure the cooperation 
and facilities generously provided by Professor E. HADORN at the University of 
Zurich, Zurich (Switzerland). For assistance in that laboratory we are indebted to 
Miss R. GLoor. For assistance during other parts of the program we owe thanks to 
Mrs. T. SuEoKA, M. Tatcot and Mrs. A. MITCHELL. 
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