I N the last decade the theoretical consequences of the joint effects of recombination rate and fitness interactions between loci have been studied by KIMURA (1956, 1965) , KOJIMA (1959' a,b), LEWONTIN and KOJIMA (1960), LEWONTIN (1964 a,b.c), andFELSENSTEIN (1965). Several observations support the relevance of this body of theory to natural and laboratory populations. Non-random associaticins of inversions in natural populations may be the result of fitness interaction between the inversions (LEVITAN, 1958;LEVITAN and SALZANO 1959;STALKER 1960; WHITE, LEWONTIN and ANDREW 1963). Viability interactions between inversions have been demonstrated experimentally ( SPASS-KY, DOBZHANSKY and ANDERSON 1965