162 T, THOMSON FLYNN 



result of this penetration is the tendency to form occasional 

 cytoblastic islands, containing usually one or two nuclei, 

 isolated by the growth round and behind them of the allantoic 

 capillaries (fig. 24). 



Stage 4 . P e r Hi m e 1 e s o b e s u 1 a , 8-8-75 mm. 



Of this stage I have no material available, so will content 

 myself by stating that Hill's figures (1897, figs. 15 to 21) show 

 that the various processes of allantoic placental formation 

 which have been initiated in the case of the younger embryos 

 can be recognized as being continued in this. 



The growth of the plasmodiblast has gone on apace, with 

 a corresponding diminution of the amount of maternal tissue 

 contained in the diploplasma. This results in a very homo- 

 geneous appearance of the tissue of the placental area. In 

 Hill's figures very few syncytial nuclei are recognizable with 

 certainty. On the other hand, it can be seen unmistakably 

 that, by this time, most of the cytoblast has been converted 

 into plasmodiblast. and that in this formation giant multi- 

 nucleate cells are a very prominent and characteristic feature 

 (see especially his fig. 17). 



Here again the greatest activity is being shown towards 

 the centre of the placental area. Of the still remaining basal 

 cytoblast cells Hill says (p. 414), ' in some cases they are multi- 

 nucleated ... or the single nucleus is also hypertrophied and 

 vesicular,' a statement which well accords with the facts to 

 which I have already drawn attention in the preceding pages. 



Many of these remaining cytoblast cells have the appearance 

 of diplokaryocytes. Some of them plainly show a tendency 

 towards plasmodial formation, as can be seen in Hill's fig. 21, 

 where the cell marked ch.ect. has very much the appearance 

 of a giant cell with plasmodial processes. 



Stage 5. Perameles obesula, 12-5 mm. 



Of this stage I possess five consecutive sections stained in 

 haematoxylin and eosin. 



Here, as before, I will confine myself to a description of the 



