108 Embryonic Development of Ovary and Testis of Mammals 



tion to these two processes is that by which the fine chromatin threads 

 in the nuclei of the oocytes at the synapsis stage of their development 

 frequently break down into a powder-like mass of very fine granules. 

 This is no doubt another process of degeneration. 



On the side of the ovary facing the mesonephros, there are a num- 

 ber of invaginations of the peritoneum (Text Fig. 3). These often 

 appear as hollow tubules that extend for some distance into the 

 ovary. At points along their extent they are found to be solid, their 

 cells being similar to those of the cords of Pfliiger. In fact they are 

 to be interpreted as such. Transition regions are found in which the 

 peritoneal lining of these hollow tubules is found to contain a greater 

 and greater percentage of primitive sex cells (Plate VII, Fig. 25) 

 up to the condition of the solid portions of the tubules where the 

 lumen is entirely obliterated by the enlargement of the peritoneal- 

 cells to form primitive sex cells. 



15 cm. Embryo. Female. — In this ^stage the above described hol- 

 low egg-tubes of Pfliiger, while still most common around the hilum, 

 are also found in the region of the cortex furthest from the mesen- 

 tery. They penetrate more deeply into the tissue of the ovary than 

 in the preceding stage, some of them extending into its very center, 

 where they could be readily mistaken for" rete tubules by persons who 

 might have studied these structures in ether forms, such as the cat. 

 There is no mistaking their identity, however, because they bear no 

 resemblance to the true rete tubules and because they were readily 

 followed through the series to their point of union with the peri- 

 toneum. These invaginations may arise either from deep grooves or 

 from the smoother surfaee of the peritoneum. At this stage the 

 medullary cords are still further reduced, no young follicles being 

 found among them. 



The mass of rete tissue is now found to be constricted at its point 

 of entrance into the ovary. Further development of the sex cells and 

 of the intra-ovarian rete has caused the boundaries of the rete cords 

 to become obscured. 



Male. — In the male, the glomeruli connected with the rete tissue 

 have degenerated to such an extent that the rete tubules are now 

 found to be in almost direct contact with the mesonephric tubules. A 

 minute description of the seminiferous tubules of this stage will 

 serve to unify the points touched upon in the preceding pages 

 (see Plate 'Y , Fig. 18). They are still solid, yet their tubular nature 

 is shown by the arrangement of the dense peripheral layer of nuclei 

 belonarinff to the fferminative cells. Each nucleus is attached to the 



