102 Embryonic Developmeut of Ovary and Testis of Mammals 



Numerous stroma cells are found to have become highly modified. 

 The cytoplasmic portions increase in amount, becoming clearly marked 

 off from surrounding cells, a centrosphere and centrosome appear, 

 and the nucleus becomes rounded, while its chromatin network stains 

 deeply. In general they assume a certain resemblance to primitive 

 sex cells, yet the nucleus shows marked differences in its smaller size 

 and more deeply-staining chromatin network. They differ also in the 

 fact that their cytoplasm becomes granular and in later stages con- 

 tains droplets of fat. These modified stroma elements are the inter- 

 stitial cells. They are very numerous in the testis and very rare in 

 the ovary. In both sex glands they divide by mitosis. A large por- 

 tion of the stroma nuclei do not undergo this transformation into 

 interstitial cells, but become elongated and take on the character of 

 connective tissue. In all iDrobability these are the cells whose nuclei 

 were smallest in the preceding stage where a difference in size and 

 appearance of the stroma nuclei was noted. Particular stress should 

 be laid upon the fact that the interstitial cells appear contemporane- 

 yiusly with the process of fatty degeneration in the sex cords and that 

 they show points of resemblance to the primitive sex cells. The latter 

 point is particularly significant in view of the fact that in the 1.8 cm. 

 embryo the nuclei of the stroma were to all appearances similar to 

 those of the germinative cells of the sex cords which were in some 

 cases developing into primitive sex cells. This would lead to some very 

 attractive hypotheses; but one should be cautious about drawing hasty 

 conclusions from such points of mere resemblance. 



3 cm. Embryo. — There are no essential differences between the rete 

 of ovary and testis. The rete cords are still being formed, their points 

 of connection with the peritoneum persisting along the entire length 

 of the rete rudiment in both sexes. Another point common to both 

 sexes is the degeneration of certain Malpighian corpuscles of the an- 

 terior part of the mesonephros. Those lying nearest to the rete cords 

 are especially affected, suffering a decrease in size and a consolidation 

 of the capillaries contained in them. 



Primitive sex cells are being formed in the rete cords from the 

 syncytial cells that have retained the primitive character exhibited by 

 the peritoneal cells, from which these cords arise. This development 

 of undifferentiated peritoneal derivatives to form primitive sex cells 

 is probably homologous with the process by which the germinative 

 cells of the seminiferous tubules of the testis and the cells of 

 the cords of Pflliger of the ovary are being transformed into 

 primitive sex cells. The sudden impulse to renewed activity in the 



