WOLFFIAN BODY. 



245 



of the anterior nephrotomes there arise rounded elevations which grow 

 posteriorly and unite with one another to form a longitudinal cord of cells 

 on either side of the body. This later becomes hollow and is known as 

 the Wolffian duct. In a rabbit embryo it is shown in Fig. 276, A. As the 

 Wolffian duct extends posteriorly it lies so close to the ectoderm that the 

 latter has been said to participate in its formation. Finally it reaches and 

 fuses with the entodermal allantois. The posterior nephrotomes are not 

 thought to contribute to the formation of the duct. As seen in Fig. 276, B, 

 they become separated both from the segments (my) and the coelomic 



mes.seg. 



,W.d. u.v. 



neph. 



FIG. 276. A, TRANSVERSE SECTION OP A RABBIT EMBRYO OF NINE DAYS; B, HUMAN EMBRYO, 4 MM.; 



C, HUMAN EMBRYO, 10 MM. 



ao, Aorta; c., posterior cardinal vein; coe., coelom; gl. f glomerulus: g. r., genital ridge; int., intestine; 

 mes., mesentery; mes. seg., mesodermic segment; my., myotome; nch., notochord; neph., nephro- 

 tome; s-c. v., subcardinal vein; si., sinusoid; sy., sympathetic nerves; u. v., umbilical vein; W. d., 

 Wolffian duct; W. t, Wolffian tubule. 



epithelium. The nephrotomes form vesicles (W.t.) which become tubular 

 and coiled; each acquires connection with the Wolffian duct (Fig. 276, C). 

 By branching or fission the tubules become more numerous than the cor- 

 responding segments. 



The aorta sends a succession of branches to the ventro-median border 

 of the Wolffian body. There they terminate in round knots of capillaries 

 known as glomeruli (Fig. 276, C). A glomerulus is at first lodged in a 

 cup shaped depression on one side of a Wolffian tubule, at its blind end. 

 The tubule then grows around the glomerulus so that the latter appears 



