BY JAS. P. HILL. 71 



since they represent the median vagina as ending freely and with- 

 out any connection with the connective tissue in which the 

 posterior ends of the lateral vaginse and urethra lie imbedded. 

 This tissue, with its enclosed canals, lateral and median vaginae 

 and urethra, represents the persistent posterior portion of the 

 genital cord, and just in this tissue, from analogy with I'erameles, 

 we should expect the formation of a pseudo-vaginal passage to take 

 place if such occurs in Macropods. 



Fletcher is the only observer who offers any observations on the 

 mode of origin of the direct communication in these forms, and 

 summarises his results in the following paragraph (13, Part ii. p. 

 10): — " In virgin animals of //. ruficoUis, II. dorsalis, P. jieni- 

 cillata, 0. rohustiis and 0. riifas, the direct communication did 

 not exist, but in one specimen of P. p [enicillata] and one of //. 

 ualahatus, the direct communication was in process of formation, 

 but still incomplete; and these two specimens seem to show that 

 the aperture of communication arises probably not by a mere 

 rupture of the intervening portion of the wall of the urogenital 

 canal, but by an involution of the latter canal growing backwards 

 to meet the cavity of the median portion of the vagina when the 

 latter has reached its maximum backward extension. My own 

 observations show that it is possible for the direct communication 

 to exist in virgins, while those of other observers show that this 

 actually is the case; but more usually it Avould seem to be formed 

 late in life, probably during pregnancy or at parturition." Brass 

 (4, p. 27) also remarks : " es ist wohl die Ansicht ausgesprochen 

 worden, dass dieser Durchbruch des Blindsackes gegen den Sin. 

 urog. liin zur zeit der Schwangerschaft stattfjinde, um den 

 Embryonen einen bequemeren Weg nach aussen zu verschaffen." 



Although I have no direct observations of my own to offer on the 

 formation of this direct communication in these forms, yet in view 

 of the occurrences in Peraineles, I feel unul^le to accept Fletcher's 

 suggestion that the direct communication is ever completed 

 independently of the median vagina, by an involution of the uro- 

 genital sinus. Convinced as I am, from the study of the condition 

 in Perameles, that the formation of the direct passage involves 



