GEN1TO -URINARY SYSTEM OF THE EMBRYO. 249 



In both sexes a new tube is developed parallel with the 

 Wolffian duct. This is the Mullerian duct. In the female it 

 is connected with the peritoneal cavity, and persists as the 

 Fallopian tube and uterus. In the male it disappears in 

 large part. The persistence of the anterior part gives rise to 

 the hydatid of Morgagni. The posterior part may remain as 

 Weber's organ. In some cases the whole tube is found in the 

 adult male, and then is known as Rathke's duct. 



The way in which the head of the epididymis conies to be 

 connected with the testis tubules has been determined in pigs' 

 embryos and in man (MacCallum). It is well known that the 

 seminiferous tubules in some of the lower vertebrates (fishes, 

 etc.) carry the sexual products over into the Malpighian cor- 

 puscles of the urinary organ, and are taken to the outside 

 through the urinary ducts. A somewhat similar condition has 

 been observed in the embryos of pigs and man. The testis 

 which develops from the peritoneal covering of the Wolffian 

 body is at all times closely connected with this organ. Tubules 

 develop in the testis, and at a certain period grow out through 

 the tissue connecting the two organs, and break into the cap- 

 sules of the Malpighian corpuscles of the Wolffian body. 

 These tubules are very fine and form a dense network. Their 

 lumina become continuous with that of Bowman's capsule, and 

 in this way a communication is established between the tubules 

 of the testis and the future epididymis and vas deferens. 



The ovary develops on the medial surface of the Wolffian 

 body in the same way as the testis. 



The permanent kidney develops as a knob-like growth at the 

 end of the primitive ureter, posterior and dorsal to the Wolffian 

 body. The exact course of the development of the kidney 

 tubules has not been worked out satisfactorily. They arise in 

 the beginning as long diverticula from the end of the ureter, 

 which grow out to the periphery of the organ and divide into 

 two branches, which arch backward toward the hilurn to join, 

 after many convolutions, with the Malpighian corpuscles. The 

 exact origin of the kidney lobule and of the various segments 

 of the uriniferous tubule is not known. 



