THE PLACENTATION OF PERAMELES. 427 



this stage is shown in fig. 35. It will be there seen that the 

 median pseudo-vaginal passage {med. p.) is simply a cleft-like 

 space in the central connective tissue of the strand^ b'^'^S 

 dorsally to the urethra (wr.) and between the lateral vaginal 

 canals (vag. I.). Its walls are entirely formed by the connec- 

 tive-tissue core of the strand, and they exhibit no histological 

 differentiation into coats, muscular or other. The passage is 

 of somewhat varying outline, with a greatest long diameter of 

 about r2 mm., and a short diameter of '6 mm. In this cleft 

 together with the allantoic stalks there occur masses of coagu- 

 lated blood (c. bl.), especially abundant along the dorsal 

 portion of the passage, where indeed the clot in certain sec- 

 tions forms a definite ovalish mass almost as large as the 

 allantoic stalks, and partially separated from the rest of the 

 passage by an imperfect fibrous septum. This clot, however, 

 is continuous anteriorly and posteriorly with that present in 

 the main subdivision of the channel, and also with the extrava- 

 sated blood so abundantly present in the surrounding connec- 

 tive tissue (fig. 35, c. bl.). The allantoic stalks (fig. 35, all. 

 s.) are somewhat oval in outline, and measure "3 mm. by 2 

 mm. in diameter. They are now in process of histological 

 degeneration. In the centre of each the cells appear clear and 

 vesicular, and the nuclei are for the most part quite dege- 

 nerate ; marginally they stain very deeply. The allantoic 

 vessels are either empty or are partly occupied by degenerat- 

 ing, mainly enucleated, foetal blood-cells, together with a 

 granular deeply staining detritus. Their endothelial lining 

 has disappeared, and their mesodermal wall is enucleated and 

 fibrous-looking. In some sections the allantoic canal can be 

 indistinctly made out, but no longer with an entodermal 

 lining. 



Direct observations of the parturition phenomena in Mar- 

 supials are by no means numerous. I know of only three 

 accounts: — (1) Owen (16, p. 721) quotes from a paper by 

 Rennger to the effect that in Didelphys azara^ the youno 

 "in gestation make the circuit of the lateral canals in which 

 they are found to be deprived of their foetal envelopes ;" (2) 



