DEVELOPMENT 



457 



body) also contribute to the excretory duct system. In the male, they per- 

 sist in part (10 to 15) to form the ductuli elTerentes; several muy become 

 vestigial forming thus the ductuli aberronti-s, the paradidyinis and the 

 appendix epididymis. In the female, these ducts early disappear for the 



Kidney f- 



Miillerian duct 



Genital gland ' ~ 

 Mesonephros 



Ureter 



Inguinal ligament 



Mesonephric due' 

 Miillerian duel 



--.1 pi .r of bladder 

 - Bladder 



-- - Opcm ng of ureter 



( Opening of mesoneph- 



\ ric i /art 



( Opening of Miillerian 



\ duct ' 

 Rectum 



Urogenital sinus 

 Cloaca 



(Icnital tubercle 

 - <!> n it'll riiltjr 

 Opening of cloaca 



FIG. 420. DIAGRAMS ILLUSTRATING THE METAMORPHOSES OF THE INDIFFERENT 

 (A) UROGENITAL SYSTEM INTO THE MALE (B), AND FEMALE (C) SYSTEMS. (From 

 Polak, after Hertwig.) 



most part a variable number persisting as vestigial structures : the epo- 

 ophoron and the paroophoron. 



The seminiferous tubules (including the recti and rete tubuli) of the 

 testis arise as solid cords of cells eontinuoiis with the peritoneal epithelial 

 covering of the gonad, and apparently as derivatives of this so-called 'ger- 

 minal epithelium.' These cords subsequently acquire a lumen, and connect 

 with the efferent tubules. In the ovary likewise such cell cords (sex-cords) 

 appear, continuous with the peritoneal (germinal) epithelium; from these 

 develop the ovarian follicles with their ova, as will be described below. 

 The relation of the extra-regional 'primordial germ-cells' to the germinal 

 epithelium and to sex-gland derivatives, discussed in the next section, 



