Gametogenesis and sex-determination gall-gly, neuroterus lenticularis (spathegaster baccarum ).—part III

Abstract

In two previous papers on the maturation of the eggs and spermatozoa and determination of sex in Neuroterus lenticularis I showed (1) that any individual female of the agamic generation produces either male or female offspring, but not both; (2) that the eggs of some agamic females undergo a reduction division at maturation, while those of others do not; (3) that, since males have 10 chromosomes in the germ-cells before maturation, while females have 20, the eggs which undergo reduction produce males, and those which do not, produce females; (4) all eggs of the sexual generation undergo a double maturation division, and are fertilised, giving rise to females of the agamic generation with 20 chromosomes in the ovarian cells. The maturation divisions in the eggs of the sexual generation were described as of a rather peculiar type, and some difficulty was experienced in forming a clear and connected idea of the process. One important problem remained unsolved—the nature of the difference between the male-producing and female-producing females of the agamic generation. No difference was discernible between the flies of the two types, nor could any difference be found between their chromosome-groups in the ovarian divisions. A tentative suggestion was made that the difference might depend on the existence of two kinds of spermatozoa, one of which might cause the fertilised egg to develop into a male-producing, the other into a female-producing agamic female, and this suggestion seemed to gain some support from the fact that in the spermatogenesis an extra-nuclear body was observed not to divide at the single spermatocyte division, but to pass over into one of the two spermatids.