96 Embryouic Development of Ovary and Testis of Mammals 



crowding which in some places is so great as to bring about the for- 

 mation of actual peritoneal invaginations which extend into the 

 stroma and frequently come in contact with the attenuated capsules of 

 Bowman. 



Peritoneal invaginations arising in the sex gland rudiment (com- 

 pare Plate II, Figs. 5 and 6) by the same process of crowding are 

 more diffuse, and more numerous than in the rete. Another dif- 

 ference between these two regions of the genital ridge is found in the 

 fact that the sex gland invaginations do not in any case reach as de^p 

 as the capsules of Bowman, the stroma being thicker in this region 

 than in the rete rudiment. 



In many cases the stroma cells are assuming the character of con- 

 nective tissue. Primitive sex cells are present in the peritoneum 

 and in the peritoneal invaginations and stroma of both rete and sex 

 gland rudiments. Their number has increased in the sex gland rudi- 

 ment, while they have shown little or no numerical increase in the 

 rete region. 



1.25 cm. Embryo. — Although the rete rudiment has increased but 

 little in thickness, the peritoneal invaginations of the rete region, which 

 may now be termed rete tubules, are much further developed than in the 

 preceding stage. The sex gland rudiment, on the other hand, has in- 

 creased greatly in thickness. Its peritoneal invaginations (sex cords) 

 have also increased in length and in number. Their nature can be best 

 understood by referring to Plate II, Fig. 5. In this and in later stages 

 the nuclei are still attached to the basement membrane which is in 

 fact formed, as we have seen, from protoplasmic processes connected 

 with them. So closely are the sex cords placed that there are very 

 few stroma cells between them. No clear cases of such are seen in 

 this figure. Such, however, are present and form in part the rudi- 

 ment of the intertubular stroma so prominent in later stages. There 

 is no doubt tbat this stroma from time to time receives additions from 

 cells which pass through the investing membrana propria of the sex 

 cords. 



The sex cords are tubular invaginations of the peritoneum and their 

 membrana propria are accompanying infoldings of the basement mem- 

 brane as seen in earlier stages (Plate I, Fig. 4 and Plate II, Fig. 5). 

 The sex cord nuclei are connected with the membrana propria by fine 

 fibrils which apparently hold them in position. 



In its earliest stage, this is a true process of invagination, but in 

 the later stages it is only apparent because of the fact that the sex 

 cords grow at their points of attachment to the peritoneum (centrifu- 



