THE ABDOMEN 687 



vas aberrans, vesicula seminaJis, and common ejaculatorj- ducts are all de- 

 veloped from the Wolffian duct. 



The interstitial stroma of the testis is developed from the mesoderm of the 

 genital ridge. The tunica albuginea is formed from connective tissue de- 

 rived from ' the basal nuclei of the sex-cords.' 



Development of the Ovary. — The embryonic rudiments pertaining to the 

 development of the ovary are as follows: 



Genital ridge and germinal epithelium. 

 Egg-columns or egg-tubes of Medullary cords. 



Pfluger (sex-cords). 



Rete-cords. 



The ovary, like the testis, is developed from the indifferent sexual orgain. 

 Whilst in the case of the testis the anterior or sexual tubules of the meso- 

 nephros or Wolffian body and the Wolffian duct pertain to its development, 

 inasmuch as the excretors- tubules of the male sexual gland are associated 

 with the epithehum of their Malpighian corpuscles ; in the case of the ovary 

 the Wolffian tubules and the Wolffian duct become vestigial. 



The ovary is developed from the sexual cords and the mesoderm of the genital 

 ridge. The epithelial cells of the genital ridge, as in the male, constitute the 

 germinal epithelium. The deep cells of the epithehum of the sex-gland region 

 of the genital ridge invade the mesoderm of the ridge, and are disposed as 

 cellular cords, which are separated by ingrowths of connective tissue, derived 

 from the mesoderm of the genital ridge. These cellular cords cire called the 

 egg-columns, or egg -tubes of Pfluger (sex-cords). These egg-columns con- 

 sist of small epithehal ceUs (foUicular cells) and large sexual cells or primitive 

 ova. They become separated from the epithehum of the genital ridge when 

 the somewhat indefinite tunica albuginea of the ovary is formed from the con- 

 nective tissue derived from ' the basal nuclei of the medullary- cords.' 



The sexual cells of the egg-columns increase in size, and each column, 

 being invaded by connecti\e tissue, is thereby broken up into groups of cells, 

 known as cell-nests, which form the primary Graafian folhcles. Each of 

 these folhcles consists of one sexual cell, or primitive ovum, and numerous 

 small epithehal cells, with an external investment of connective tissue. 

 These small cells are disposed as a single layer around the o\-um, which layer 

 represents the membrana granulosa, and the investing connective tissue 

 forms the theca folliculi. At a later period the cells of the membrana granu- 

 losa undergo prohferation, and so give rise to several layers. A fluid, called 

 liquor folliculi, is then formed by these cells; the o\Tim is thereby displaced 

 to one side of the foUicle; and the mass of cells, within which it is embedded, 

 forms the discus proligerus. 



The egg-columns (egg-tubes of Pfliiger) form the cortical part of the ovary. 



The medullary Cor(£, which contribute to the medullary part of the ovary, 

 hke the sex-cords of the testis, are probably developed from the germinal 

 epithehum of the sex-gland region of the genital ridge. They bear a re- 

 semblance to the egg-columns, bj" which they aire succeeded, and contain 

 follicular cells and primitive ova. They become broken up into a number 

 of primary- Graafian folhcles, but these soon degenerate. In the meduUar)- 

 part of the ovary they give rise to groups of foUicular cells, and these subse- 

 quently become converted into connective tissue. 



The rete-cords are developed, as in the male, from the germinal epithehum 

 of the rete-region of the genital ridge. They differ from the rete-cords of the 

 male inasmuch as they do not become hollow, so as to form tubules, but 

 remain solid. They resemble the medullary cords, and, along with the re- 

 mains of these cords, they form the medullary part of the ovarj', giving rise 

 to groups of foUicular cells, which subsequently become converted into con- 

 nective tissue. This arrangement is known as the rete ovarii. 



The epithehum, which covers the surface of the ovary, in adult hfe repre- 

 sents the superficial cells of the germinal epithelium, which take no part in the 

 formation of the egg-columns. The ceUs of this epithehum differ in a marked 

 manricr from those of the adjacent peritoneum inasmuch as they are columnar, 

 whilst the adjacent cells are the usual endothelial cells of a serous membrane. 



