874 



DEVELOPMENT 



[CH. L7X. 



-Transverse section of embryo chick (third day), mr, Rudimentary spinal cord ; the primitive 

 1 canal has become constricted in the middle; c/i, notochord ; uwh, primordial 



FIG. 674. T . 



central canal has become constricted in the middle; cb, 'notochord ; uwh, primordial vertebral 

 mass; 771, muscle-plate; dr, df, hypoblast and visceral layer of mesoblast lining groove, which is 

 not yet closed in to form the intestines; ao, one of the primitive aortas; un, Wolffian body ; ung, 

 Wolffian duct; v c, vena cardinalis ; li, epiblast; hp, somatopleur and its reflection to form a /, 

 amniotic fold ; p, pleuro-peritoneal cavity. (Kolliker.) 



FIG. 675. Section of intermediate cell-mass on the fourth day. m, Mesentery; L, somatopleur; a', 

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



