656 DEVELOPMENT OF THE KIDNEYS. 



tremities in small rounded dilatations. Into each of these dilated 

 extremities is received a globular coil of capillary bloodvessels, or 

 glomerulus, similar to that of the adult kidney. The tubules of the 

 Wolffian body all empty into a common excretory duct, which leaves 

 the organ at its lower extremity, and communicates afterward with 

 the lower part of the intestinal canal, just at the point where the 

 diverticulum of the allantois is given off, and where the urinary 

 bladder is afterward to be situated. The principal, if not the 

 only distinction, between the minute structure of the Wolffian 

 bodies and that of the true kidneys, consists in the size of the 

 tubules and of their glomeruli, these elements being considerably 

 larger in the Wolffian body than in the kidney. In the foetal 

 pig, for example, when about an inch and a half in length, the 

 diameter of the tubules of the Wolffian body is 2 /, of an inch, 

 while in the kidney of the same foetus, the diameter of the tubules 

 is only ^\^ of an inch. The glomeruli in the Wolffian bodies 

 measure ^ of an inch in diameter, while those of the kidney mea- 

 sure only y^ of an inch. The Wolffian bodies are therefore urinary 

 organs, so far as regards their anatomical structure, and are some- 

 times known, accordingly, by the name of the "false kidneys." 

 There is little doubt that they perform, at this early period, a func- 

 tion analogous to that of the kidneys, and separate from the blood 

 of the embryo an excrementitious fluid which is discharged by the 

 ducts of the organ into the cavity of the allantois. 



'Subsequently, the Wolffian bodies increase for a time in size, 

 though- not so rapidly as the rest of the body ; and consequently 

 their relative magnitude diminishes. Still later, they begin to 

 suffer an absolute diminution or atrophy, and become gradually 

 less and less perceptible. In the human subject, they are hardly 

 to be detected after the end of the second month (Longet), and in 

 the quadrupeds also they completely disappear long before birth. 

 They are consequently foetal organs, destined to play an important 

 part during a certain stage of development, but to become after- 

 ward atrophied and absorbed, as the physiological condition of the 

 foetus alters. During the period, however, of their retrogression 

 and atrophy, other organs appear in their neighborhood, which 

 become afterward permanently developed. These are, first, the 

 kidneys, and secondly, the internal organs of generation. 



The kidneys are formed just behind the Wolffian bodies, and are 

 at first entirely concealed by them in a front view, the kidneys 

 being at this time not more than a fourth or a fifth part the size of 



