THE WOLFFIAN DUCT AND BODY. 



589 



Each Wolffian body consists at first of rods of cells, which 

 appear to arise independently of the Wolffian duct. The rods 

 soon become S-shaped : early in the fourth week they acquire 

 axial cavities, and so become tubes ; and by the end of the week 

 the tubes, or Wolffian tubules as they may now be termed, grow 

 towards the Wolffian duct and open into it. The opposite, or 



NS 



MT 



FIG. 248. Transverse section across the body of a Human Embryo, estimated 

 as fourteen days old. For a figure of the whole embryo, see Fig. 185, 

 p. 481. The embryo had thirteen pairs of mesoblastic somites, and the- 

 section figured passes through the tenth pair. (From Kollmann.) x 240. 



A, aorta. C, coelom. CH, notochord. Q-T, mid-gut. KG, Wolfflan duct. ME,- 

 somatopleuric layer of mesoblast. MH, splanchnopleuric layer of mesoblast. MT, 

 myotome or mesoblastic somite. M"C, central canal of spinal cord. M"S, spinal cord. 



closed ends of the tubules become dilated, and then invaginated 

 to form Malpighian bodies, the glomeruli being derived from 

 branches of the aorta which penetrate into the Wolffian body 

 along its whole length ; while the veins open into the large- 

 posterior cardinal veins, which are intimately associated with the 

 Wolffian bodies from their first appearance. 



The Malpighian bodies are more abundant along the inner 

 side of each Wolffian body, while the duct lies along its outer 

 border, except at the hinder end, where it crosses to the inner side. 



During the second month the Wolffian bodies grow rapidly :: 



