CHAPTER XV. 



DEVELOPMENT OF THE WOLFFIAN BODIES, KIDNEYS, 

 AND INTERNAL ORGANS OF GENERATION. 



THE first trace of a urinary apparatus consists of two elongated, 

 fusiform organs, which make their appearance in the abdomen at 

 a very early period, one on each side the spinal column, known as the 

 Wolffian bodies. They are fully formed, in the human embryo, toward 

 the end of the first month (Coste), at which time they are the largest 

 organs in the abdomen, extending from just below the heart nearly to 

 the posterior extremity of the body. In the foBtal pig, when thirteen or 

 fourteen millimetres in length, they are rounded and kidney-shaped, and 

 occupy a large part of the abdominal cavity. 



Their combined weight is a little over three FlG - >229t 



per cent, of the entire body ; a proportion seven 

 or eight times as large as that of the kidneys in 

 the adult condition. There are at this period 

 only three organs of noticeable size in the abdo- 

 men, namely, the liver, at the upper part of the 

 abdominal cavity ; the intestine, which is already 

 somewhat convoluted, and occupies a central 

 position ; and the Wolffian bodies on each side 

 the spinal column. FtETAL * 13 millimetres 



m , TTT i* i- T XL j.- long; the abdominal walls 



The Wolffian bodies, in their intimate structure, cut awayi to show the posi _ 

 closely resemble the adult kidney. Thev consist tion of the Wolffian bodies. 

 of secreting tubules, lined with "epithelium, run- ^ h .TVosL^ u^ 

 ning transversely to the outer edges of the organs, 4. Wolffian body, 

 where they terminate by rounded dilatations. 



In each of these dilated extremities is a globular coil of capillary blood- 

 vessels, similar to the glomerulus of the kidney. At the inner edge 

 of the Wolffian body the tubules empty into a common excretory duct, 

 which leaves the organ at its lower extremity, and communicates with 

 the intestinal canal, at a point where the urinary bladder is afterward 

 situated. The principal distinction in structure, between the Wolffian 

 bodies and the kidneys, consists in the size of their tubules and glorn- 

 eruli. In the foetal pig, when three or four centimetres in length, the 

 tubules of the Wolffian body are 0.125 millimetre in diameter; while 

 those of the kidney in the same foetus are only 0.034 millimetre. The 

 glomeruli of the Wolffian bodies are 0.55 millimetre in diameter, while 

 those of the kidney measure only 0.14 millimetre. The Wolffian bodies 

 are therefore urinary organs, so far as regards their minute structure, 



681 



