Article summarizes conclusions from 20 yrs. of work. Intersexuality in these moths depends chiefly on general sex genes, of which M for maleness is in the X chromosome (Z of many authors), and F for femaleness is maternally inherited (probably through the Y, or W, chromosome, though this involves assumption that F exerts its whole initial influence before the reduction division). Many multiple allelomorphs of F and M, differing in strength, have been found in different races of moths. Within a single pure race, F and M correspond in strength and produce only normal [male][male] (FMM) and [female][female] (FM). When weak and strong races are crossed in certain ways, bringing about indecisive ratios of F to M or F to MM, intersexes are produced, in varying degrees of intermediacy up to complete sex reversal in both directions. Sex-reversal [male][male] have been shown by their progeny to be of XY genetic composition. Corresponding proof that sex-reversal [female][female] are XX has not been obtained, owing to the poor viability and sterility of such [female][female]. Several auto-somal factors modifying intersexuality have been found. Intersex starts its development as of the sex denoted by its chromosomes, but changes sooner or later to opposite sex development. When this turning point occurs depends on relative strengths of F and M; early occurrence produces high degree, late occurrence low degree, of intersexuality. Embryonic development confirms this view, in general, since, with the exception of antennae, the organs differentiated early are changed little in the intersexes, those differentiated late are changed much. Strength of genes is held to be due to quantity; alternative theories of plus and minus modifiers are rejected.