68 FEMALE UROGENITAL ORGANS OF PERAMELES, 



the false passage must he reformed at each parturition, and the 

 same also holds true for the extreme posterior end of the passage 

 over a greater or lesser extent. 



The allantoic stalks left behind in the anterior portion of the 

 median passage after each parturition very soon completely dis- 

 appear from the uteri and median vaginae, but portions of them 

 remain recognisable in the upper portion of the pseudo-vaginal 

 passage for a relatively very long time. The fate of these stalks 

 has been traced in the preceding pages. They have been shown 

 to undergo histological degeneration and to become surrounded 

 and invaded by the adjacent connective tissue, a process resulting 

 in their complete conversion into fibrosed masses and their final 

 incorporation in the surrounding connective tissue. As regards 

 the formation of the pseud o- vaginal portion of the median passage, 

 I pointed out in my previous paper that it is " formed either 

 just before or at the first act of parturition " (3, p. 429). I am 

 now inclined to believe that the latter period is tlie correct one 

 and that the passage is simply formed by the embryo as it passes 

 down, as a longitudinal cleft-like rupture of the very vascular 

 connective tissue core of the urogenital strand. "That some such 

 rupture does occur is evidenced not only by the appearance of the 

 false passage, but also by the pretty extensive extravasations of 

 blood found both in and surrounding the track followed by the 

 foetus during its egress, i.e., the median pseudo- vaginal passage" 

 (p. 429). At all events, I am unable to conceive of the formation 

 of such a cleft-like passage other than in association with the 

 downward passage of the young during parturition. As to the 

 formation of the common median vagina, the separateness of the 

 median vaginal cul-de-sacs in specimen ix. suggests that the dis- 

 appearance of their common partition wall posteriorly ma}'^ like- 

 wise be due to the passage of the young into their narrow posterior 

 ends, resulting in pressure on, and subsequent rupture of, the 

 common wall, which is, no doubt, in a stretched and congested 

 condition during the act of parturition. In my pi'evious paper (3) 

 I instituted a comparison between the median pseudo-^'aginal 

 passage in Perarneles and the epithelially lined median vaginal 



