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Show 288 MR. F. E. BEDDARD ON THE [May 4, V. Postembryonic Origin of Ova. This section has been added after tbe rest of the paper was in type; it deals with the results of some further observations which tend to confirm the supposition hinted at above, that the ovary of Lepidosiren contains ova of two kinds which have a different mode of development. It should have been mentioned that the general surface of the ovary is, for the most part, devoid of any germinal epithelium, a condition which is often met with in adult ovaries ; in places, however, the germinal epithelium is very conspicuously present and in a condition of active multiplication. These patches of germinal epithelium are only occasional, as has also been noticed by Spengel1 in the case of the Frog's ovary ; I have only succeeded in discovering them after this paper was communicated to the Society. I have been able, however, to insert a figure into Plate XXVIII. (fig. 7), which illustrates the fact that the germinal epithelium has not entirely disappeared in the mature ovary. In every case that I observed, the germinal epithelium, where it was left, was in a state of very active cell-division ; the cells on the surface of the ovary were closely crowded together, and had given rise to a mass of cells three or four deep, surrounding a cavity partly filled by another mass of cells of a somewhat different appearance. The central mass of cells was invariably connected at one side only with the surrounding sphere, as shown in the figure (Plate XXVIII. fig. 7), and, at this point, its cells gradually alter in appearance until they become indistinguishable from those of the surrounding hollow sphere, which is the future follicular epithelium. The investing mass of cells (f) is connected by a pedicle with the germinal epithelium (e) on the outside of the ovary, and is clearly formed by a proliferation and inward growth of its cells. The arrangement of these, as shown in the figure, gives a strong impression of motion; the cells look as if they had been arrested in the act of rapid proliferation inwards. The cells of the germinal epithelium, both those on the surface of the ovary and those which form the investing mass of the central cells, are small, but with large, deeply-stained nuclei. On the other hand the cells which occupy the interior of the sphere are much larger, and of a somewhat irregular, angular contour, and often containing more than one nucleus. As already stated, these cells pass by gradations into the follicular mass at one side only, but this may be due to shrinkage. On the outside of the central mass of cells, and forming generally a complete peripheral layer round them, is an amorphous mass (x) deeply stained by the reagent; here and there nuclei, with or without some surrounding protoplasm, were imbedded in this amorphous mass, which thus has the appearance of being formed by the fusion of the peripheral layer of the central cells. I have no observations to offer as to the origin of the central mass of cells ; but their position and attachment to the peripheral layer, more particularly at one point, would seem to suggest that they arise, like 1 Sempcr's ' Arbeiten,' Bd. iii. |
