DEVELOPMENT OF THE WOLFFIAN BODIES, ETC. 785 



at which time both organs coexist, the diameter of the tubules of the 

 Wolffian body is 0.125 millimetre, while in the kidney of the same foetus, 

 the diameter of the tubules is only 0.034 millimetre. The glomeruli in 

 the Wolffian bodies measure 0.55 millimetre in diameter, while those of 

 the kidney measure only 0.14 millimetre. The Wolffian bodies are there- 

 fore urinary organs, so far as regards their anatomical structure, and 

 are sometimes known by the name of the " false kidneys." There is 

 little doubt that they perform, at this early period, a function analogous 

 to that of the kidneys, and separate from the blood of the embryo an 

 excrementitious fluid which is discharged into the cavity of the allantois. 



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

 not so rapidly as the other organs. Their relative magnitude con- 

 sequently diminishes. Still later, they suffer an absolute atrophy, and 

 become gradually less perceptible. In the human embryo, they are 

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

 in the quadrupeds they completely disappear long before birth. 



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 one-fourth or one-fifth part the size of the 

 Wolffian bodies. (Fig. 293.) The kidneys 

 subsequently enlarging, while the Wolffian 

 bodies diminish, the proportion between the 

 two organs is reversed ; and the Wolffian 

 bodies appear as small rounded masses, sit- 

 uated on the anterior surface of the kidneys. 

 (Figs. 294 and 295). The kidneys, during 

 this period, grow more rapidly in an upward 

 than in a downward direction, so that the 

 Wolffian bodies come to be situated near 

 their inferior extremity. 



The kidneys, during the succeeding pe- 

 riods of foetal life, become in turn very largely 

 developed in proportion to the rest of the author's possession. i. Woif- 

 internal organs ; attaining a size, in the foetal fian body> 2> Kidne y- 

 pig, equal to more than two per cent, in weight of the entire body. 

 This proportion again diminishes before birth, owing to the increased 

 development of other parts. In the human foetus at birth, the weight 

 of the two kidneys, taken together, is 6 parts per thousand of that of 

 the entire body. 



Internal Organs of Generation. About the same time that the kid- 

 neys are formed behind the Wolffian bodies, two oval-shaped organs 

 make their appearance in front, on the inner side of the Wolffian bodies 

 and between them and the spinal column. These bodies are the inter- 

 nal organs of generation ; namely, the testicles in the male, and the 

 ovaries in the female. At first they occupy the same situation and 

 present the same appearance, whether the foetus is afterward to be 

 male or female. (Fig. 294.) 



