653 DEVELOPMENT OF THE KIDNEYS. 



A short distance above the internal organs of generation there 

 commences, on each side, a narrow tube or duct, which runs from 

 above downward along the anterior border of the Wolfnan body, 

 immediately in front of and parallel with the excretory duct of this 

 organ. The two tubes, right and left, then approach each other 

 below ; and, joining upon the median line, empty, together with 

 the ducts of the Wolffian bodies, into the base of the allantois, or 

 what will afterward be the base of the urinary bladder. These tubes 

 serve as the excretory ducts of the internal organs of generation ; 

 and will afterward become the vasa deferentia in the male, and the 

 Fallopian tubes in the female. According to Coste, the vasa defe- 

 rentia at an early period are disconnected with the testicles ; and 

 originate, like the Fallopian tubes, by free extremities, presenting 

 each an open orifice. It is only afterward, according to the same 

 author, that the vasa deferentia become adherent to the testicles, and 

 a communication is established between them and the tubuli semi- 

 niferi. In the female, the Fallopian tubes remain permanently 

 disconnected with the ovaries, except by the edge of the fimbriated 

 extremity ; which in many of the lower animals becomes closely 

 adherent to the ovary, and envelopes it more or less completely. 



Male Organs of Generation ; Descent of the Testicles. In the male 

 foetus there now commences a movement of translation, or change 

 of place, in the internal organs of generation, which is known as 

 the "descent of the testicles." In consequence of this movement, 

 the above organs, which are at first placed near the middle of the 

 abdomen, and directly in front of the kidneys, come at last to be 

 situated in the scrotum, altogether outside and below the abdominal 

 cavity. They also become inclosed in a distinct serous sac of their 

 own, the tunica vaginalis testis. This apparent movement of the 

 testicles is accomplished in the same manner as that of the Wolf- 

 fian bodies, above mentioned, viz., by a disproportionate growth of 

 the middle and upper portions of the abdomen and of the organs 

 situated above the testicles, so that the relative position of these 

 organs becomes altered. The descent of the testicles is accompanied 

 by certain other alterations in the organs themselves and their 

 appendages, which take place in the following manner. 



By the upward enlargement of the kidneys, both the Wolfnan 

 bodies and the testicles are soon found to be situated near the 

 lower extremity of these organs. (Fig. 249.) At the same time, a 

 slender rounded cord (not represented in the figure) passes from 

 the lower extremity of each testicle in an outward and downward 



