THE DEVBLdPMENT OP THE EMBRYO ITSELF. 115 



lining the ccelom at one region becomes differentiated into col- 

 umnar cells (germinal epithelium) which by involution into 

 the underlying mesoblast forms a tubule extending from before 

 backward and in close relation with the WolflBan duct, thus 

 forming the MuUerian duct by the process of cleavage and 

 separation referred to previously. 



Fig. 123.— Diagrammatic representation of the genital organs of a hnman embryo pre- 

 vious to sezual distinction (Allen Tliomson). W, Wolfflan body; gc, genital cord; 

 m, MflUerian duct; w, Wolffian duct; ug, urogenital sinus; cp, clitoris or penis; 

 I, intestine; d, cloaca; Is, part from which the ecrotam or labia majora are devel- 

 oped; o(, origin of the ovary or testicle respectively; a;, part of the Wolffian body 

 developed later into the coni vasculosi; 3, ureter; 4, bladder; 5, urachus. 



The future of the Miillerian and Wolfflan ducts varies ac- 

 cording to the sex of the embryo. 



In the male the WoM&an duct persists as the vas deferens ; 

 in the female it remains as a rudiment in the region near the 

 ovary (hydatid of Morgagni). In the female the Miillerian duct 

 becomes the oviduct and related parts (uterus and vagina) ; in 

 the male it atrophies. One, usually the right, also atrophies in 

 female birds. The sinus pocularis of the prostate is the remnant 

 in the male of the fused tubes. 



The various forms of the generative apparatus derived from 

 the Miillerian ducts, as determined by different degrees of fu- 



