Abstract
The agent which causes the sterility of the hybrid males in crosses between certain strains of D. paulistorum can be transmitted by injection, as well as througlfthe egg cytoplasm. Females of the Mesltas strain were Injected with homogenates of flies from the Santa Marta strain, or of Santa Marta [female] X Mesltas [male] hybrid flies. The injected females were crossed to Mesltas males. Their progenies must have had pure Mesitas genes, but the males In these progenies were nevertheless sterile. Injection of Santa Marta females with similar homogenates leads to no sterility.