VII.—Spermatogenesis inDrosophila pseudo-obscuraFrolowa. II. The Cytological Basis of Sterility in Hybrid Males of Races A and B

Two races or physiological species (A and B) were found inDrosophila pseudo-obscuraby Lancefield (1922), who described later (1925, 1929) the genetical behaviour of the interracial hybrids. The present writer (1931, 1932,a, b) has reported further investigations concerning the sterility of the male and the regional reduction of crossing-over in the female of the interracial hybrids. The results obtained suggested that there are genetic fertility factors, located in the sex chromosome complex, which are primarily responsible for the sterility of the F1males. A similar conclusion has been reached more recently by Dobzhansky (1933b) from his cytological studies of hybrid males.