Growth and Maturation in the Parthenogenetic Eggs of Daphnia magna Strauss

Abstract

1. The parthenogenetic egg develops from one of a group of four cells, of which the remaining three become nurse cells. These degenerate, presumably supplying the egg with nutritive material, but are never engulfed by it. 2. Associated with these phenomena is the appearance in the egg cytoplasm of a body resembling in appearance the “degenerate body” previously described in Moina macrocopa. 3. The location of the chromatin during the growth period of the egg is uncertain. It is probably either in a vesicular state, or contained in the large, prominent nucleolus present in these stages. 4. The nucleolus partially disintegrates, producing a mass of granular material, which, on the basis of Feulgen's test, is not interpreted as chromatin. Neither is it considered to be nutritive material. 5. The chromatin is first visible in the prophase of the single maturation division, in the form of small granules. These exhibit an extremely irregular clumping, the significance of which is s unknown. 6. The diploid chromosome number is eight. No reduction occurs in the maturation division, the egg developing with eight chromosomes. 7. It would be desirable to investigate the possible existence of chromosomal sex differences in these eggs. This is not feasible, however, until further information is secured concerning environmental sex control in this species. © 1937, Japan Mendel Society, International Society of Cytology. All rights reserved.