818 HANbBOOK OF PHYSIOLOGY. 



permanent kidney, which constitute the substance of the Wolffian body. 

 Meanwhile another portion of mesoblast between the Wolffian body and 

 the mesentery projects in the form of a ridge, covered on its free surface 



Fig. 513. Transverse section of embryo chick (third day), rnr, rudimentary spinal cord; the 

 primitive central canal has become constricted in the middle ; c h, notochord ; uwh, primordial 

 vertebral mass; m, muscle-plate; dr, df, hypoblast and visceral layer of mesoblast lining 

 groove, which is not yet closed in to form the intestines ; a o, one of the primitive aortae ; u n, 

 Wolffian body; ung, Wolffian duct; DC, vena cardinalis; ft, epiblast; h p, somatopleure and its 

 reflection to form a/, amniotic fold; p, pi euro-peritoneal cavity. (KOlfiker.) 



with epithelium termed germ epithelium. From this projection is de- 

 veloped the reproductive gland (ovary or testis as the 'case may be). 



Simultaneously, on the outer wall of the Wolffian body, between it 

 and the body- wall on each side, an involution is formed from the pleuro- 

 peritoneal cavity in the form of a longitudinal furrow, whose edges soon 

 close over to form a duct (Miiller's duct). 



All the above points are shown in the accompanying figures, 513, 514. 



The Wolffian bodies, or temporary kidneys, as they may be termed, 

 give place at an early period in the human foetus to their successors, the 

 permanent kidneys, which are developed behind them. They diminish 

 rapidly in size, and by the end of the third month have almost entirely 

 disappeared. In connection, however, with their upper part, in the 

 male, there are developed from a new mass of blastema, the vasa effe- 

 rentia, coni vasculosi, and glolus major of the epididymis; and thus is 

 brought about a direct connection between the secreting part of the 

 testicle and its duct. The Wolffian ducts persist in the male, and are 

 developed to form the body and globus minor of the epididymis, the vas 

 deferens, and ejaculatory duct on each side, the vesiculae seminales form- 

 ing diverticula from their lower part. In the female a small relic of 

 the Wolffian body persists as iheparovarium; in the male a similar relic 

 is termed the organ of Gir aides. The lower end of the Wolffian duct 

 remains in the female as the duct of Gaertner which descends toward, 

 and is lost upon, the anterior wall of the vagina. 



