THE PLACENTATION OF PERAMELES. 425 



and are often entirely absent in the sections. It is unnecessary 

 to enter into details. 



I would simply refer to figs. 32 and 33^ and point out that 

 from the knob-like projection (a) attached to the margin of 

 the allautois [all. m.) there arise two cell layers, one from each 

 side. The one (c) may possibly be a vestige of the yolk-sac 

 splanchnopleure^ while the other {b) may similarly be a vestige 

 of the vascular omphalopleure. 



Whether this be so or not the fact remains, that besides 

 these structures no other traces of the yolk-sac were found in 

 the uterus, and this fact, taken in conjunction with the already 

 described greater de^'cneration of the syncytium outside the 

 placental area as compared with that of the latter, renders it 

 almost certain that the omphalopleure breaks up and dis- 

 appears some time previous to parturition. 



Finally I may direct attention to the cells marked ch. ect" , 

 in figs. 32 and 34, as they may possibly represent persistent 

 marginal chorionic ectoderm cells. 



Parturition. 



In fig. 25 the genital organs of this stage are shown 

 partially dissected. The left uterus (/. ut.) has been opened 

 by a ventral longitudinal incision, so as to expose the placental 

 area {pi. a.). The vaginal caeca {v. ccec.) and the bladder [bl.) 

 are pushed over to the left side, and the allantoic stalk {all. s.) 

 arising from near the centre of the inner wall of the adherent 

 allautois has been traced posteriorly. It was found to pass 

 backwards through a posterior common portion of the two uteri 

 (common uterine canal) into what sections show to be a 

 median cleft-like passage in the connective tissue lying between 

 the two lateral vaginal canals. Through this median passage, 

 or median pseudo-vaginal passage, as we may term it, it is 

 obvious that delivery must have taken place. 



At the time of making this dissection I was unaware of the 

 existence of any median passage in Perameles. Owen (16, 

 p. 683), in his short description of the female genital organs 

 of P. obesula, makes no mention of such; and, indeed, in 



