288 MR. 1 . K. BEDDARD ON THE [May4, 



V. Fostembryonic Origin of Ova. 



This section has been added after the 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 

 Leindosiren 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, how- 

 ever, 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 SpengeP 

 iu 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 in- 

 vesting mass of cells (/) 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, hut 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 

 f )rmed 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 



' Semper's ' Arbcitcn,' Ed. iii. 



