136 UNIVERSALITY OF DEGENERATIVE EVOLUTION 



opened out into the general body cavity, this was 

 Muller's duct (M.). 



c 



um 



FIG. 57. Development of the Urino-genital system in higher Vertebrates. 



A. Pronephric stage, a, tubules; c, excreting duct; ce, cloaca. 



B. Mesonephric stage. G, mesonephros; r, remains of pronephros ; c, excreting 

 canal; w, neutral genital gland ; M, Muller's duct; ce, cloaca, 



C. Metanephric or adult stage, in the male. R, permanent kidney; J7, ureter; 

 F, bladder; T, testis; e and t', epididymis and vas deferens ; s,vas deferens; 

 km, hydatid of Morgagni; h, hydatid ; p, paradidymis; um, uterus masculinus. 



D. Metanephric or adult stage in the female. R, permanent kidney ; V, ureter ; 

 F, bladder; 0> ovary; p and p', parovarium and paraophorcn; w, Weber's 

 organ ; F, vagina; , uterus; t, aperture of Fallopian tube; A, hydatid. 



The mesonephros, however, was not the perma- 

 nent kidney. In the course of time the metanephros, 

 the permanent excretory gland, was developed (fig. 



