The History of the Cytoplasmic Elements during Vitellogenesis in Drosophila melanogaster

I. At least two kinds of yolk are developed in the eggs of Drosophila melanogaster. The origin of the proteid yolk has been traced to precursors sent into the oocyte by the nurse cells, while the minute fatty yolk granules are transformed chondriomites also contributed by the nurses. The behaviour and morphology of Golgi material in the nurses indicate that it may be responsible for a third type of yolk. 2. A yolk nucleus has been found in oocytes of an age when the germinal disk has been pushed to one side. So long as such a structure exists, all the proteid yolk pre-cursors are concentrated and matured within its confine. Soon this structure dis-integrates and disappears. But after its disappearance, yolk precursors continue to be sent by the nurses into the oocyte, and there they develop into mature granules apparently without the benefit of a yolk nucleus. On the basis of facts thus far ob-tained, it is, therefore, difficult to say just what role the so-called yolk nucleus plays in vitellogenesis in Drosophila melanogaster. 3. Golgi material in the nurse cells has been observed to undergo two distinct proliferations. In young nurses, Golgi material occurs in a few discrete bits which, a