DESCRIPTION OF PLATE V— continued. 



Fig. 4. — x 50. g.f. Groups of small follicles, with a single layered 

 flattened epithelium. The nucleus of the ovum is central. That one of the 

 group nearest to a large and growing follicle has become compressed into an 

 oval shape, and this is still more the case with the members of two other 

 small groups of follicles {e.f.). g. c. Granular cells, arranged in two 

 elongated masses (remains of the Wolffian body). The reference marks de- 

 scribing the large follicle are in most cases similar to those previously 

 explained. V. C. Vesicular cells, transitional into the central substance (c. s.). 

 These cells are an addition to the intermediate layer («. I.), and are not present 

 in the largest follicles. They are swollen, unstained, with no distinct nucleus, 

 and are doubtless in a state of transition into the central substance. The 

 ovum (o) has no distinctly marked nucleus; it becomes indistinct in the 

 increase from the size shown in Fig. 3 to that shown in this fig. I have never 

 been able to detect it in the largest ovarian ova. There is a thin layer of the 

 membrana granulosa cells surrounding the ovum as in the higher Mammalia, 

 but the cells are not columnar. The central substance [c. s.) is finely granular 

 and clot-like. It has shrunk away from the membrana granulosa. In both 

 these respects it more resembles the appearances presented by the hardened 

 liquor folliculi of higher Mammalia, and in both respects the resemblance is 

 greater in younger follicles and gradually disappears as the follicles become 

 older. The present figure would fairly represent a stage in the development 

 of the Graafian follicle of higher Mammalia, except for the absence of columnar 

 cells round the ovum. In this and the succeeding figs. 5 — 7 the outer cells 

 of the granulosa should be columnar, the others more distinctly polygonal. 



Fig. 5. — X 50. A larger follicle than the last. The reference marks are 

 the same. There are still cells of the membrana granulosa round the ovum, 

 but they have no connection with the peripheral cells, thus diverging from the 

 higher Mammalian type. The central substance (c. s.) still remains finely 

 granular, but it has not shrank away from the membrana granulosa. 



Fig. 6. — x 50. An apparently full-sized follicle. Most of the references 

 are the same. The ovum (o) is now seen to be embedded in the central 

 substance (c. s.) with no traces of cells round it (occasionally they can be 

 detected). The central substance (after the use of the above-mentioned re- 

 agents) is a granular network, which stains with difficulty and does not 

 shrink away from the membrana granulosa. The fibrous tunic (/. L) is seen 

 to l.e especially densely fibrous in its outer part, and vascular within. The 

 membrana granulosa is irregularly thickened opposite to the ovum, and at this 

 point the fibrous tunic thins away so that the follicle nearly penetrates it. 

 This fact and the slight thickness which separates the follicle from the external 

 surface, together with the convexity of the latter, make it probable that the 

 follicle is ripe. The ovum is always placed (as far as I have observed) on that 

 side of the ripe follicle which is directed towards the external surface of the 

 ovary, though not always at the most convex point. The granulosa cells 



