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Show 282 MR. F. E. BEDDARD ON THE [May 4, very dissimilar to true nuclei, and the sphere has no limiting membrane. It is doubtful therefore whether they can be regarded as cells, though it is probable that, as the segmentation of the ovum advances, the white yolk is directly converted into cells. Now in the cell-like bodies which I have described in the immature ovum of Lepidosiren there is a very distinct and obvious nucleus (figs. 9-20), which is in fact entirely similar to a nucleus of one of the follicular cells ; it is deeply stained by borax carmine and unevenly stained, so that it has the appearance of being formed of a meshwork of condensed protoplasm, the interspaces of which are filled by a homogeneous substance which is less acted upon by the reagent. In some instances there was more than a single nucleus to each of these cells, but it is quite impossible to confound these nuclei with the surrounding particles of yolk. Furthermore, in many cases the limiting membrane of the cells was distinctly visible (figs. 9 &c.) ; and the fact that the cell-contents were hardly acted upon by the staining fluid rendered the perception of this membrane easier. There seems to be but little doubt that these structures are veritable cells, and are not in any way comparable to the white yolk-spheres. The question then arises, What is the origin of these cells 1 Are they formed anew within the substance of the ovum, or have they migrated from the follicle into the interior of the ovum ? The former supposition is supported by no facts that I have been able to note, and it is distinctly negatived by other facts. In the first place, these cells are very closely similar to the cells of the follicular epithelium ; like them they are bounded by a distinct limiting membrane; the contents of both consist of protoplasmic strands and numerous highly refractive particles similar to the yolk-particles ; the nucleus is identical in shape and size ; and the behaviour of both to the staining reagent is precisely the same. This series of facts would, however, be hardly regarded as proof that these cells have originated from the follicular epithelium; it might be supposed that the cells have arisen within the ovum, and that some of them have migrated to the periphery to form the follicle, as has been stated by various observers to be the case in certain other ova (see p. 276) ; but the immense vascular development round the follicular epithelium that has been already mentioned seems to indicate that the main activity is centered in these latter cells ; and this fact, coupled with the additional fact that in certain instances there were masses of migrating cells evidently in course of being budded off (Plate XXVIII. figs. 5, 6) from the follicular epithelium, seems to indicate that the second supposition as to the origin of these cells is correct, viz. that they are formed by the proliferation of the follicular cells and migrate into the interior of the ovary. The migration of these cells also explains the absence of a limiting membrane to the ovum. A "formed" membrane, however thin, would evidently prevent such a migration. It appears to me possible to make another statement as a deduction from the facts just detailed : that the follicular epithelium-cells secrete the yolk which is conveyed to the interior of the ovum by |