DEVELOPMENT OF OVARY AND TESTIS. 59 



ovary undergo similar differentiation to the medullary-cords 

 and the cords of Pfliiger forming the cortex. The rete-tissue 

 within the ovary of the 18 cm. pig embryo is found to contain 

 young follicles, each with a single layer of follicular cells ; the 

 enlarged oocyte in the center having passed through the synap- 

 sis condition, characteristic of one stage in the development of the 

 young oocytes. All such follicles subsequently degenerate. In 

 the testis the intra-glandular portions of the rete-tubules are simi- 

 lar to the seminiferous-tubules, but differ from them in their 

 much smaller diameter and in the earlier acquisition of a lumen. 

 They contain the sex cells characteristic of the seminiferous- 

 tubules. These are at first present in the extra-glandular region 

 of both ovary and testis, but disappear more or less completely 

 in later stages. No attempt was made to study out the fate 

 of the sex cells of the rete-tubules of the pig testis. They are 

 stjll present in the 25 cm. pig embryo. In the rabbit they are 

 found in the rete of the testis twenty-four days after birth, but 

 are not to be found in that of a rabbit killed 140 days after birth. 

 The rete-tubules are so completely united by anastomosis that 

 their connected lumen forms a large irregular cavity divided here 

 and there by irregular partitions formed by the walls of the sev- 

 eral rete-tubules. 



The connective tissue elements of ovary and testis are derived 

 from the peritoneum. In early stages they are not distinguish- 

 able from the cells that make up the sex-cords, except that the 

 latter are marked off from the stroma by their membrana propria. 

 As before stated, the albuginea is largely formed by actual trans- 

 formation of the basal part of the sex cords into connective tissue 

 elements. 



The interstitial cells are characterized by a large nucleus, dis- 

 tinct cell boundaries, a centrosphere and centrosome, and very 

 granular cytoplasm. They first appear in the stroma of both 

 testis and ovary of the pig of 2.5 cm. length. They are far more 

 numerous in the testis than in the ovary. Their appearance is 

 coincident with that of a large number of fatty globules in the 

 peritoneum and sex cords. In the testis they persist for a long 

 time. In the ovary, however, the few cells appearing at this 

 stage speedily disappear. In both organs they divide by mitosis. 



