Memoirs: The Rôles of the Nurse-cells, Oocytes and Follicle-cells in Tenthredinid Oogenesis

1. Ovary formation in Tenthredinidae follows the general hymenopterous plan. 2. Nurse-cell phenomena are as follows: the nuclei of the first nutritive chamber are surrounded by a chromatin cloud and many of them contain irregular darkly-staining masses of nuclear material, which masses may also be present in the riper chambers; the granules given off from the nuclei into the chromatin cloud eventually become surrounded by a vesicle and give rise to the ‘secondary’ or ‘accessory’ nuclei. 3. Oocyte nucleolar phenomena show the following: the nucleoli in Thrinax mixta and Platycampus luridiventris give rise to buds which become free; in one case buds were observed close to the inner surface of the nuclear membrane in Allantus (Emphytus) pallipes are shown what are apparently later stages of this process, viz. the passage of the buds through the nuclear membrane into the egg substance and their formation there into accessory nuclei. 4. The fate of the nurse-cells is shown in the older nutritive chambers and oocytes--the cell boundaries become indistinct and some of the cytoplasm, together with contained accessory nuclei, passes by a narrow channel into the oocyte. The cytoplasmic flow becomes more marked in the last chamber. In the final stages, shown in the last chamber, all the cells lose their boundaries and the common cytoplasm passes into the oocyte, carrying with it the free nuclei to their engulfment and absorption in the ooplasm. 5. Some of the follicle-cells surrounding the last oocyte in Pristiphora padi, and the fifth, sixth, and seventh of Thrinax mixta, contain granular dark-staining material which may completely fill the cell, these granules probably originating from the nucleus. They pass out of the follicle-cell into the egg where they become surrounded by vesicles, and, finally, present an appearance indistinguishable from that of accessory nuclei. 6. Secondary or accessory nuclei, therefore, have a threefold origin, namely, from the nuclei, of nurse-cells and oocytes and from follicle-cells, their source of derivation in the last being the follicular nuclei. 7. The follicle-cells of the distal pole of the last oocyte of one ovariole of Pristiphora padi have processes which insinuate themselves into the ooplasm. 8. The phenomena of oogenesis described in these four species of sawflies, while embracing certain which have not hitherto been recorded, conform, in essentials, with those already discovered for Hymenoptera generally.