ABSTRACT
The ultra-structure of the pole cells and oöcytes of Drosophila melanogaster, Drosophila willistoni and Drosophila virilis has been investigated.
The eggs were dechorionated in 3 per cent, sodium hypochlorite, and the vitelline membrane removed in the fixative.
Three fixatives were employed: (a) OsO4-veronal, at pH 7 · 4; (b) formol-phosphate with 7 · 5 per cent, sucrose, at pH 7 · 2; (c) gluteraldehyde, buffered at pH 7 · 4 with sodium cacodyalate. All three gave good results, but membranous structures remained rather indistinct after aldehyde fixation.
Two kinds of granule occur within the pole cells, the polar and the epsilon granules. Both types may occur together within the same cell, but one or other type tends to predominate. The functions and interrelationships of these granules are obscure.
Polar granules are spherical with a dense, granular cortex surrounding a less electron-opaque core, and lack a bounding membrane.
Epsilon granules are ovoid and a delicate double membrane surrounds the coarse fibrous matrix, in which spaces occur. Their composition is unknown.
Preliminary observations suggest that the epsilon granules arise from convolutions of the cell membranes which surround the mature oöcyte.
