78 



FEMALE UROGENITAL ORGAXS OF PERAMBLES, 



Fig. 3. 



behind the openings of the ureters into the fundus of the bladder; 



while fig. 3 represents a section through the cord at a somewhat 



lower level. They may be com- 

 pared, respectively, with tigs. 

 5 and 8, Plates iii.-iv., repre- 

 senting sections through the 

 corresponding regions of the 

 genital organs in the adult, 

 when it will at once be 

 apparent that, so far as con- 

 cerns the general disposition 



and course of the genital ducts, these remain in a condition 



which can only be described as persistently embryonic. 



Now, in young foetal Macropods, the genital ducts have essen- 

 tially the same disposition as in the fatal and adult rerainelei>, 

 i.e., the posterior portions of the uterine and the entire vaginal 

 segments of the MiiUerian duct and the urethra lie imbedded in 

 a common mass of mesodermic tissue — the genital cord. In 

 both, the uterine segments pass back side by side to open into 

 small median vaginal cul-de-sacs, arising at the junction of the 

 former with the vaginal sections of the MiiUerian ducts. From 

 the cul-de-sacs, the lateral vaginal canals continue directly for- 

 wards and outwards ventral to the uterine segments of the ducts 

 (text-fig. 2, a.vag.c), in order to sharply bend round anteriorly 

 and to continue backwards. Just behind the bend the two lateral 

 canals are widely separated from each other by the ureters. 

 These pass in mesially to the vaginal canals to reach the base of 

 the bladder, which is imbedded ventrally in the tissue of the 

 genital cord. Behind this level, the two vaginal canals gradualh^ 

 appro.ximate and finally (text-fig. 3) run back parallel with each 

 other and with the Wolffian ducts (w.d.) and urethra (u7'eth.) to 

 open into the short urogenital sinus. While, then, in Perameles, 

 the genital ducts persistently retain their position in the genital 

 cord, in Macropods they later become more or less free from the 

 tissue of that cord. 



