306 



ESSENTIALS OF ZOOLOGY 



capsules and each receives a glomerulus. The original duct 

 is the ureter. 



The germ cells appear in a genital ridge formed medially 

 to the mesonephros. The peritoneal epithelium becomes 

 infolded, carrying with it the germ cells. In the case of the 

 male these form the tubules of the testis, and they become 

 connected with a number of the mesonephric tubules. The 

 tubules of the testis thus open into the mesonephros, which is 



Somite 



Spinal cord 

 Notochord 



Aorta 



Endoderm 



Pronephric duct 

 Mesoneph. tubule 



Splanchnocoel 



Pronephric duct 



Boumari's 



FIG. 143. Transverse section of a more advanced stage through a developing 

 mesonephric tubule, and (below) a diagram of a mesonephric tubule at 

 a later stage. 



the Wolffian body or epididymis, and the mesonephric duct 

 or Wolffian duct becomes the vas deferens. The ducts con- 

 necting the epididymis with the testis are called the vasa 

 efferentia. 



In the female, the corresponding foldings of the germinal 

 ridge form the follicles containing the ova. The duct is a special 

 formation. In front of the mesonephros a thickening of the 

 peritoneum develops a groove which forms an opening into 

 the peritoneal cavity and, fusing posteriorly, grows backwards 

 close to the Wolffian duct. This is the oviduct or Miillerian 

 duct. The anterior internal opening becomes the internal 

 opening of the Fallopian tube, and the duct forms the Fallopian 

 tube and the uterus. It fuses with its neighbour caudally, 



