THE DEVELOPMENT OF THE URINO-GENITAL 

 SYSTEM. 



The urinary and genital sj'Stems are closely allied in their 

 origin and are both preceded by the Wolffian bodies and ducts, 

 which for a time perform the excretory office of the kidneys and 

 finall}^ take prominent parts in the origin of both the urinary 

 and genital organs. 



The Wolffian Ducts and Wolffian Bodies. 



The Wolffian ducts are claimed by some embryologists to orig- 

 inate, as a pair of longitudinal grooves, in the epiblast on the 

 lateral surface of the body, at about the level of the notochord 

 or somewhat below. The invaginations of epiblast continue to 

 sink inward into the me.soblast of the somatopleure until they 

 attain the inner surface of the body cavity, in contact with the 

 peritoneum. Other investigators, and apparently the majority, 

 hold that the Wolffian ducts are wholly of mesoblastic origin, 

 though at first lying immediately against the epiblast, as solid 

 rods; which later become excavated in their center to constitute 

 their cavity. For a time the Wolffian ducts end blindly be- 

 hind, but later they open into the cloaca. 



The Wolffian bodies are first recognizable, during the third 

 week of the embryo, as longitudinal thickenings in the dorsal 

 surface of the body cavity, there being one of these ridges on 

 either side of the mesentery. They develop rapidly and become 

 greatly elongated so that they soon reach from the posterior por- 

 tion of the cervical region back to the end of the lumbar region. 



The essential tissues of the Wolffian bodies appear to develop, 

 independently of the Wolffian ducts, from the mesoblast, in the 

 form of rods and cells. The rods coil somewhat upon them- 

 selves and become excavated to constitute tubes and, growing 

 toward the Wolffian duct, empty into it at one end, while the 

 other end becomes dilated, and then invaginated, to constitute 

 the Malphigian bodies, or glomeruli. Into these glomeruli, 

 branches of the aorta penetrate to furnish the functional blood 

 supply. The veins from these glands empty into the posterior 

 cardinal veins. 

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