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Show 512 MR. F. E. BEDDARD ON THE DEVELOPMENT AND [Dec. 7, contact with the interior mass of cells, the follicular layer being such points indistinguishable. It is possible that the difference of size in the nuclei corresponds to a distinction between "primitive ova" and "germinal cells" such as has been described by Semper, Balfour, and so many writers in other Vertebrata ; in this case the larger nuclei will be the primitive ova. This suggestion must be of course only regarded as such ; I have no real evidence to offer except the different size of the nuclei. In very many instances a degeneration of the nuclei could be observed. This takes place in several ways, some of which may be stages in the same series. Some of the nuclei (figs. 14, 17) remain of the same size and shape as the normal nuclei, but show a much paler colour and fewer nucleoli; in one instance (fig. 15) I observed a commencing disintegration of the nucleus, the substance of which appeared to be in a condition of solution at one point where it passed gradually into the substance of the cell, the limiting membrane of the nucleus being here invisible. In other cases (figs. 19,20) the nuclei are as darkly stained as the normal nuclei or even rather more so, but instead of presenting a uniform oval contour, the nucleus was variously contorted and irregular in shape. The centre of the mass, however, is not entirely occupied by cells like those that have just been described. There is a certain amount of an amorphous substance (fig. \,p), well stained with the borax carmine, which lies in patches between some of the central cells, and particularly on the outside, in the space which separates them from the follicular layer. This substance is of an homogeneous appearance, though lighter in colour in some regions than in others ; it is rather more abundantly developed in the stage next to be described than in the present (cf. fig. 9, Plate LIIL). This substance encloses patches of cells, or sometimes single cells; occasionally the protoplasm of the cells has undergone a certain change at the periphery, where it gradually passes into the homogeneous mass surrounding it; frequently scattered nuclei are to be found imbedded in it, and a comparison of these nuclei with those of the central cells shows them to be identical. The general appearance of the homogeneous substance suggests a coagulated fluid, and it is very like the liquor folliculi of the Mammalian ovum coagulated by alcohol ; but this substance cannot be excreted by the central cells or by the follicular cells, because it contains numerous traces of them in the shape of free nuclei with or without a certain amount of partially altered protoplasm attached. These facts rather indicate that the substance in question is produced by the alteration and fusion into a semifluid mass of some of the central cells. This mode of formation is, however, not opposed to a comparison with the Mammalian liquor folliculi, which has been asserted by some to have a similar origin ; the great difference is that this semifluid substance has the power of forming yolk, as will be seen after the description of the later stages. There are other bodies which seem to be referable to the stage just described, though differing in certain structural particulars as well as in their smaller size. |