CHAPTER XIII 



THE URINOGENITAL SYSTEM 



The history of the pronephros and the origin of the meso- 

 nephros have been already described (Chap. VI). We have now 

 to consider (1) the hiter history of the mesonephros, (2) the 

 development of the metanephros or permanent kidney, (3) the 

 development of the reproductive organs and their ducts, and 

 (4) the development of the siiprarenals. All these organs form 

 an embryological unit, b}^ virtue of their mode of origin and their 

 interrelations. Thus we find that the intermediate cell-mass is 

 significant for the development of all: its growth causes the forma- 

 tion of the Wolffian body, on the median face of which the gonads 

 arise. The secreting tubules and renal corpuscles of the perma- 

 nent kidney are also derivatives of the intermediate cell-mass. 

 The Wolffian duct is derived from the same source, and by change 

 of function becomes the vas deferens, after functioning for a while 

 as the excretory duct of the mesonephros. Certain parts of the 

 mesonephros also enter into the construction of the testis. And 

 the Miillerian duct, which forms the oviduct of the female, is 

 derived from the epithelium covering the Wolffian body. 



I. The Later History of the Mesonephros 



In Chapter VI we traced the origin of the nephrogenous 

 tissue, and the differentiation of the first mesonephric tubules 

 within it. We saw that in each of the segments concerned a 

 number of balls of cells arises by condensation within the neph- 

 rogenous tissue, and that these become converted into vesicles. 

 We saw also tliat each vesicle sends out a tubular sprout from 

 its lateral side to the Wolffian duct, with which it unites; and 

 that its median face becomes converted into a renal corpuscle. 

 These processes take place sucessively in antero-posterior order 

 within the somites concerned, so that a series of stages in the 

 development of the tubules may be studied in the same embryo. 

 Moreover, all the tubules of a given somite do not develop simul- 



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