THE ORGANS OF THE MIDDLE GERM-LAYER. 



387 



the four ducts are united behind the bladder (hbl) into a fascicle, the 

 genital cord this union is due to their becoming surrounded, by the 

 umbilical arteries which have at this time attained a large size, and 

 which run from the aorta on both 

 sides of the bladder up to the 

 umbilicus and to their being, as 

 it were, tied up into a bundle by 

 them. In a cross section through 

 the genital cord (fig. 228) we find 

 the mesonephric ducts (ug) some- 

 what more anterior [ventral] and 

 at the same time farther apart 

 than the Miillerian ducts (ing), 

 which are a little behind them 

 and pressed quite close together 

 in the median plane. 



In older embryos there arise 

 in the evolution of the urogenital 

 system differences between the 

 two sexes which are visible even 

 externally and which become 

 more distinct from month to 



month. These result from fundamental metamorphoses, which the 

 whole apparatus continually undergoes in its separate parts. In 

 connection with this some originally quite large fundaments undergo 

 almost complete degeneration; of those which remain some are 

 serviceable only in the female, others only in the male ; when not 

 employed, they disappear. Moreover the conditions which were 

 referred to at the beginning of the description are extensively altered 

 by the fact that the sexual organs surrender their original position, 

 on either side of the lumbar vertebrae, and move farther downward 



Fig. 220. Urinary and sexual organs of a 

 human embryo 8 weeks old. after KOL- 

 LIKER. Magnified about 3 diameters, and 

 seen from the ventral side. 



nn, Right suprarenal body ; un, primitive 

 kidney ; n, kidney ; ung, mesonephric 

 duct ; gk, HUNTER'S directive or inguinal 

 ligament (gubernaculnm Hunteri or liga- 

 mentum uteri rotundum) ; m, rectum ; 

 b, bladder ; kd, sexual gland. 



into the pelvic cavity. 



I describe first the changes in the male, then those in the female. 



(A) The Metamorphosis in the Male. Descensus testiculorum. 



Whereas the testis (figs. 221 and 222) by conglomeration of the 

 seminal tubules becomes a bulky organ (A), the mesonephros (nh + pa) 

 is retarded in its development more and more, and is at the same 

 time differently metamorphosed in its anterior and its posterior 

 portions. The anterior or sexual part of tJie primitive kidney (nh), 



