THE WOLFFIAN BODIES. 



807 



system as a wliole has its Inundation in the mesoblastic layer. In birds 

 and mammals the duct, which is first formed, appears in its commence- 

 ment as a sohd cord in the upper part of a group of cells, projecting 

 below the epiblast, in the interval between the protovertebral mass and 



Fig. 603. — Kidneys, Wolffia>- Bodies, Wolffian Fi^r. 603. 



AKD MtJLLERIAN DuCTS OP A FtETAL BiRD. 



Magnified (after J. Miiller). 



a, kidney ; 5, tuliular part of Wolfflan body : c, 

 the ovary ; d, suprarenal body \ e, ureter ; /, Wolf- 

 fian duct ; g, duct of Miiller. 



the united somatopleure and splanchno- 

 pleure of the mesoblast, and thence called 

 the mtermcdiate cell mass (fig. GOO, vnfi). 

 This cord becomes hollow, and gradually 

 changes its place by sinking downwards 

 in the cellular mass in which it is imbedded, 

 towards the pleuro-peritoneal cavity, while 

 the tubular and glomerular structures of 

 the Wolffian body are developed as diverti- 

 cula from the duct in connection with 

 the neighbouring cellular blastema. 



The intermediate cell-mass now forms a 

 considerable projection to the outside of 

 the mesentery, which occupies a median 



position (figs. 602 and C04), and the epithelium on its surface exhibits a 

 considerable thickening in two places, first, along the inner side, where 

 it becomes columnar, and forms an opaque whitish ridge, the //«'we^;//7itf- 

 lium, the seat of after formation of the primitive ovigerms ; and second, 

 along the outer side in a line inside the seat of the Wolffian duct, where, 

 by a process of grooved involution, there is gradually formed the duct 

 named Miiller ian, after its discoverer, Johannes Miiller. It is now fully 

 ascertained that both the Wolffian and Miillerian ducts are constantly 

 present in all embryoes of birds and mammals, whatever the sex they 

 may be destined afterwards to assume ; but the respective ducts have a 

 difterent sexual destination, for the duct of ]\lUller becomes converted 

 into the oviduct of the female, while in the male the Wolffian duct 

 forms the vas deferens, or main seminal duct of the testicle ; and 

 while vestiges of the duct of Miiller are perceptible in the developed 

 male, remains of the Wolffian duct are almost always present in the 

 female in a manner afterwards to be described. 



The permanent kichicijs of birds and mammals take their origin in 

 connection with the Wolffian duct and formative substance deposited 

 near the Wolffian bodies. Their first rudiments consist in a diver- 

 ticulum from the upper or dorsal aspect of the Wolffian duct near its 

 posterior extremity, which constitutes the commencement of the ureter ; 

 and from this the tubular and glandular parts of the kidney are formed 

 by extension into the neighbouring mass of blastema at a period 

 somewhat later than that of the development of the Wolffian body itself. 



The researches of Waldeyer and others have shown that the procluc- 

 iive glands of the generative organs in the two sexes, ovary and testis, 

 arise from nearly the same part of the intermediate cell mass, but in 



