EMBRYOLOGY OP THE MARSUPIALIA. H 



bilaminar omplialopleure (PI. 2, fig. 8, ect.) is just about 

 double as thick as that of Stage C. The cells are large and 

 somewhat irregular in shape, with projecting outer ends. 

 Their protoplasm is considerably vacuolated. In Didelphys, 

 according to Selenka (3, pp. 137 and 138), the ectodermal cells 

 of both the vascular and bilaminar omphalopleure undergo 

 enlargement during the last two days of intra-uterine life. 

 Selenka regards the enlargement of these cells as associated 

 with their functional activity in transmitting the secretion of 

 the uterine glands into the yolk-sac, but here again I am 

 inclined to look upon the hypertrophy as a sign of degenera- 

 tion. 



The entoderm of the bilaminar omphalopleure is a very 

 much thinner layer than the ectoderm, and consists of flat- 

 tened attenuated cells (PI. 2, fig. 8). 



III. Genital Organs. — As I have already given elsewhere i 

 an extended account of the structure of the urogenital organs 

 and of the main phenomena connected with the act of parturi- 

 tion, a brief resume of some of the results of that portion of 

 my investigation will here suffice. 



The female of the present stage proves to have been in 

 her first pregnancy, as shown by the condition of the genital 

 organs. 



Each uterus passes back and opens into a short blindly 

 ending canal, the median vaginal cul-de-sac, which is 

 externally not marked off from the uterus, while internally 

 the OS of the latter is exceedingly ill-defined, a condition 

 which led me in my previous paper to misinterpret the 

 vaginal cul-de-sacs as posterior prolongations of the uteri. 

 The two vaginal cul-de-sacs, separated by a common partition 

 wall, lie embedded in the connective tissue of the anterior end 

 of the urogenital strand between the lateral vaginal canals, 

 here bent slightly outwards. From the anterior ventral end 

 of each cul-de-sac, just below the opening of the uterus, there 

 passes forwards in the connective tissue underlying the 

 posterior portions of the uteri (uterine necks) the anterior 



> ' Proc. Linn. Soc. N.S.W.,' March, 1899. 



