1494 THE OVAKY. [BOOK iv. 



which the cumulus proligerus projects. If the follicle be a 

 smaller one the fluid may be very scanty, or absent altogether, 

 there being no distinction between the cumulus and the rest of the 

 membrana granulosa, of which the former is merely a part. If 

 the follicle be very small, as in the case of the majority of those 

 forming the germinal zone, the membrana granulosa will be 

 reduced to a single layer of cells surrounding the ovum, the zona 

 pellucida will be absent, and the investment of stroma will be 

 very delicate, but the ovum will still be recognized by its large 

 cell-substance and its already conspicuous nucleus or germinal 

 vesicle. 



931. In a ripe or nearly ripe follicle of a human ovary, the 

 ovum measures about *2 mm. in diameter. The cell body may be 

 considered as consisting on the one hand of undifferentiated 

 protoplasmic cell-substance which, as in so many other cases, 

 presents a reticulate appearance under the influence of reagents, 

 and on the other hand of a multitude of refractive spherules 

 or granules of varying size imbedded in the former and con- 

 stituting the yolk proper. These yolk granules, which are 

 more scanty in the immediate neighbourhood of the germinal 

 vesicle and at the periphery of the cell-substance than elsewhere, 

 are, if we may judge by analogy from the results of the examina- 

 tion of eggs such as that of the hen in which the yolk is 

 massive, largely composed of three chemical substances, namely, 

 of vitellin, which is a proteid having the general characters of the 

 globulin group but also special features of its own, of lecithin 

 ( 71) and of the ill-understood substance or substances known 

 as nuclein ( 29). The chemical history of the yolk is however at 

 present very imperfectly known; but we may conclude that the 

 yolk granules if they do nothing else, at least serve as food 

 material of a highly nourishing character for the real living 

 substance of the ovum. The zona radiata may probably be 

 regarded as a cuticular product of the cells of the cumulus, the 

 surfaces of which next to it are irregular, presenting numerous 

 delicate processes. In some animals at least the striae are due to 

 minute canals occupied by minute threads of a protoplasmic 

 nature which probably serve to establish continuity between 

 the cell-substance of the follicular cells and that of the ovum; 

 but it appears doubtful whether, at least in the ripe follicle, 

 these canals are present in the human ovum, and it is maintained 

 that in the ripe ovum not only is the inner surface of the zona 

 smooth but that a space containing fluid always exists between 

 it and the surface of the ovum. There can be no doubt that 

 the cells of the cumulus do in some way feed the ovum; but 

 if no canals are present in the zona radiata, we may infer that the 

 material is conveyed through the zona in a dissolved state, and 

 that the yolk granules are formed by a subsequent activity of the 

 cell substance of the ovum comparable to that which leads to the 



