THE UROGENITAL SYSTEM 



441 



begin to disappear, and a new cortical zone is formed, probably derived 

 from the peritoneum. Rows of primordial ova known as Pflueger's 

 egg tubes extend through the cortex to the medulla. Their arrangement 

 suggests that the egg-tubes are proliferated from the peritoneal epithelium, 

 which therefore is known as germinal epithelium. In late fetal life the 

 primordial ova become surrounded by indifferent follicular cells and 

 differentiated as the definitive ova. The changes in the Graafian follicles 

 have already been described (p. 421). Medullary cords and a rete ovarii 

 comparable with the testis cords and rete testis appear as transient 

 structures in the ovary. 



Reproductive Ducts. The mesonephric or Wolffian ducts are utilized 

 by the male as reproductive ducts, the ductus deferentes. Mueller's 



CORTNER'S DUCT) 



Fig. 368. 



-Diagrams of the testis (A) and ovary (B) showing the homologies of their 

 components. (Redrawn after Mall modified.) 



ducts are also developed in both sexes. Each Mueller's duct arises from 

 a longitudinal groove on the lateral side of the mesonephros. The 

 peritoneal epithelium sinks into the underlying mesenchyma. Except 

 at its anterior end, where it remains open as the ostium tubae, the groove 

 closes over and grows posteriorly as far as the cloaca into which it acquires 

 an opening. 



Male Reproductive Ducts. In a three month embryo, the anterior 

 and posterior regions of the mesonephros differ. In the anterior region, 

 which consists of five to twelve renal tubules, the collecting portions 

 of the tubules separate from the excretory portions and acquire connexion 

 with the tubules of the rete testis. In this manner, anterior mesonephric 

 tubules form the ductuli deferentes and serve as outlets for the secretion 

 of the testis. The remaining, posterior, portion of the mesonephros 

 mostly degenerates, remnants persisting as the paradidymis and ductuli 

 aberrantes. The cranial portion of the mesonephric duct increases 

 greatly in length to form the ductus epididymidis. The posterior portion 

 becomes the ductus deferens. 



In the male, Mueller's ducts begin to atrophy in the third month. 

 In the adult, remnants of the anterior and posterior extremities may 



