THE URO-GENITAL SYSTEM. 105 



invagination of the epiblast and comes to lie subsequently in the 

 intermediate cell mass (Fig. 85). Thus it will be seen that the 

 lining of the Wolffian duct and of the structures formed from it, 

 are epiblastic in nature and liable to all the diseases to which 

 epiblastic structures are subject. 



The Pro-nephros (Fig. 79).— Even before the meso-nephros 

 (Wolffian body) there appears to have been another kidney — the 

 pro-nephros. While only permanently functional in some of the 

 lowest fishes and even in them it is partly replaced by the meso- 

 nephros, it still appears transiently in the embryos of vertebrates 

 and is said to occur also in the human embryo. It is developed 

 in the cervical region at the anterior end of the Wolffian ridge. 

 Like the Wolffian body it is composed of a longitudinal duct and 

 tubules ; the duct appears to be an anterior prolongation of the 

 Wolffian duct but its tubules are different. They open into the 

 coelom (peritoneal cavity) by trumpet-shaped ciliated ends, and 

 are derived from invaginations of the mesothelial lining of the 

 coelom. They are coiled and terminate in the pro-nephric duct, 

 an anterior continuation of the Wolffian. A glomerulus is 

 developed in the course of each pro-nephric tubule (Fig. 79). 

 The pro-nephric tubules are probably representatives of the 

 segmental (nephridial) tubules of the Vermes. 



The Fate of the Wolffian Body (meso-nephros) and Pro- 

 nephros. — (1) In the Female. 



In Fig. 81 are shown the various remnants of the embryonic 

 renal formations which may persist in the adult female. The 

 Mullerian duct, the upper part of which becomes the Fallopian 

 tube, is situated in the Wolffian ridge (Fig. 80). Hence when 

 the ovary and tube migrate to the pelvis, the Wolffian mesentery, 

 which comes to form the meso-salpinx, is also drawn within the 

 pelvis and with it all the Wolffian remnants in the female. A 

 hydatid attached to the meso-salpinx (part of the broad ligament) 

 at the fimbriated extremity of the Fallopian tube (Fig. 81) is 

 situated at the anterior end of the Wolffian duct and represents 

 the most anterior (cephalic) of the Wolffian tubules or perhaps 

 the cephalic end of the Wolffian duct, or even the pro-nephros, 

 although it is improbable that this transient embryonic structure 

 should persist (J. H. Watson). It certainly corresponds to the 

 pro-nephric remnant found in the frog. It may become enlarged 



