MORPHOGENESIS OF THE MAMMALIAN OVARY 367 



portion of the medulla and in the intermediate zone. Interspersed 

 with these are cords or clusters of follicle cells whose connection 

 with egg cells is not apparent. Some of these appear to come from 

 the indifferent cells of the egg cord in its breaking up, or to have 

 survived the degeneration of an egg cell which they once envel- 

 oped (fig. 16). Such epithelial structures with the surrounding 

 stroma and the interstitial cells compose the epithelio-stromal 

 nucleus of the two-week ovary. Marked growth of the masses 

 and cords of follicular cells and of the stroma produces the ovary 

 of two months. Very great irregularity is shown in the growth 

 of the cords of follicle cells, and their relation to the ova is par- 

 ticularly interesting. A typical follicle formation of this period 

 is shown in figures 24 and 25. 



It is structures of this kind that have been interpreted by von 

 Winiwarter and Sainmont as follicles in degeneration attended 

 by penetration of the stroma and enucleatioti. Figures 16 to 

 25 are introduced in illustration of the reverse view. From 

 the morphological relations there shown it would appear that 

 the eggs are becoming enveloped by the growing follicle masses. 

 Figure 16 shows two small egg cells of smaller size and close to 

 each a cluster of follicle cells, doubtless derived from adjacent 

 indifferent cells of the original egg cord. Each egg is invested by 

 a laj^er of follicle cells of its own. By growth of the follicular 

 cluster the ovum, in its epithelium, becomes partially surrounded 

 (fig. 17, 18) and finally completely invested (figs. 19, 20) by the 

 growing cell mass; and with the appearance of an antrum— indi- 

 cated from the beginning — a Graafian follicle more or less irreg- 

 ular, is developed. Several ova may thus become included in a 

 single follicle which may be of rather tubular form (fig. 23) . The 

 layer of follicle cells belonging to the ovum and immediately 

 surrounding it may be traced well into the complete investment. 

 The investing mass fuses with it and its identity is finally lost. 

 It is indicated in figures 17 to 21. 



Whether the investing folUcular mass at the beginning is al- 

 ways or even usuall}^ distinct from the sheathing follicle cells 

 is not easy to determine. In many instances, at least, it would 

 appear that the investing mass is developed from one side of the 



