858 



DEVELOPMENT. 



[CH. LVIII. 



them. Each diminishes rapidly in size, and loses all renal 

 functions. In the male it is developed into the vasa efferentia, 



Fig. 678. Transverse section of embryo cluck (third day), mi; rudimentary spinal cord : 

 the primitive central canal has become constricted in the middle ; ch, notoehord ; 

 u w h, 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 aortse ; u n, Wolffian body ; u n g, Wolffian duct ; v c, vena 

 cardinalis; h. epiblast ; hp, somatopleur and its reflection to form nf, amniotic fold ; 

 p, pleuro-peritoneal cavity. (Kiilliker.) 



Fig. 679. Section of intermediate cell-mass on the fourth day. m, mesentery ; L, somato- 

 pleur ; a, germinal epithelium, from which z, the duct of Miiller. becomes involuted ; 

 i, thickened part of germinal epithelium in which the primitive ova and o, are 

 lying ; E, modified mesoblast, which will form the stroma of the ovary ; WK, Wolffian 

 body ; y, Wolffian duct. X 160. (Waldeyer.) 



