Contents

01 July 1983
Vol 221, Issue 4605

About The Cover

Four-winged fly (Diptera) produced by combining three mutants of the bithorax gene complex in Drosophila. The haltere-bearing or third thoracic segment closely resembles the wing-bearing or second thoracic segment as the result of reduction in function of three genes of the complex: abx, bx3, and pbx. See page 23. [E. B. Lewis, California Institute of Technology, Pasadena 91125]