218 THE FOURTH DAY. [CHAP. 



FIG. 72. 



Two SECTIONS SHEWING THE JUNCTION OF THE TERMINAL 

 SOLID PORTION OF THE MULLERIAN DUCT WITH THE 

 WOLFFIAN DUCT. 



In A the terminal portion of the duct is quite distinct ; in B 

 it has united with the walls of the Wolffian duct. 



md. Miillerian duct. Wd. Wolffian duct. 



walls of the Wolffian duct, it may grow backwards from 

 cells derived from that duct. 



The Miillerian duct finally reaches the cloaca though 

 it does not in the female for a long time open into it, 

 and in the male never does so. 



The anterior part of the commencing Miillerian duct with its 

 three openings into the body-cavity is probably homologous with 

 the head kidney or pronephros of the Ichthyopsida. 



Permanent kidney or metanephros. Between the 

 80th and 100th hour of incubation, the permanent kid- 

 neys begin to make their appearance, and as is the case 

 with the Wolffian bodies, the first portion of them to 

 appear is their duct. Near its posterior extremity the 

 Wolffian duct becomes expanded, and from the expand- 

 ed portion a diverticulum is constricted off which in a 



