796 THE EXCRETORY AND REPRODUCTIVE SYSTEMS 



the medullary zone into the cortical zone of the ovary. These columns 

 establish the septa ovarii. The septa ovarii branch distally, dividing 

 the cortical zone into columns and compartmental areas of germ and 

 epithelial cells. 



The proliferation of sex cords (Pfluger's cords) may continue from the 

 germinal epithelium for an extensive period in certain mammals, such as the 

 cat. De Winiwarter and Sainmont ('09) noted three successive periods, al- 

 though Kingsbury ('38) was unable to find a clear-cut distinction between 

 the first and second proliferation. In the developing opossum, active prolifera- 

 tion from the germinal epithelium may be observed up to a time just previous 

 to the fourth month, following birth (Nelsen and Swain, '42). 



At an early stage of development, the primitive ovary in transverse section 

 presents the following features (fig. 3501): 



( 1 ) an outer proliferating germinal epithelium; 



(2) a primitive tunica albuginea beneath the germinal epithelium, com- 

 posed of epithelial and germ cells together with some connective tissue 

 elements contributed by the ovarian septa; 



(3) the primitive cortex, a compact layer within the primitive tunica albu- 

 ginea, composed of masses of germ cells, egg cords, and epithelial 

 elements, together with strands of differentiating mesenchymal cells. 

 The mesenchymal strands from the ovarian septa segregate the egg 

 cords into separate areas of germ cells and epithelial elements; 



(4) internally, near the mesovarium or the peritoneal support of the ovary, 

 is the primitive medulla composed of epithelial cells, mesenchyme, 

 blood vessels, and some oocytes and oogonia; 



(5) in the region of the mesovarium is a compact cellular mass, the rudi- 

 ment of the rete ovarii, the homologue of the rudiment of rete testis 

 in the male. The fundament of the rete ovarii continues rudimentary, 

 but a framework of connective tissue is established in this area of 

 the ovary similar to that of the mediastium in the testis, and 



(6) from the area of the rete ovarii, radiating strands of mesenchymal 

 cells, extend peripherally through the medulla and into the cortex, 

 and thus establish the sepia ovarii, i.e., septa of the ovary. Certain rela- 

 tively large "interstitial cells" appear in the septula areas. 



2) Formation of the secondary cortex and medulla. During later stages in 

 ovarian development the following changes are effected: 



(1) The primitive tunica albuginea becomes converted into a relatively 

 thick secondary tunica albuginea lying between the germinal epithelium 

 and the cells of the cortical zone. It contains connective-tissue fibrils 

 and fibers of larger dimension, together with mesenchyme and con- 

 nective tissue cells. The changes in the developing tunica albuginea 



