PLACENTA IN PERAMELES 155 



cells with distinct- cell outlines. The cytoplasm is granular 

 and the nuclei large and plump. Their chromatin contents 

 are in the form of an extremely rich network with a number 

 of karyosomes. A nucleolus may be present, and if so is of large 

 size. At the edge of the placental area the cytoblast (cyt.) 

 passes over into the ectoderm of the marginal chorion, whose 

 cells gradually decrease in size till they attain, at the junction 

 with the vascular omphalopleure, the normal dimensions and 

 appearance of trophol)lastic ectoderm cells. Some idea of the 

 difference in size of the cells of this l-Ajer may be obtained from 

 the fact that, at the margin of attachment, the cells are twice, 

 while in the centre of the area of attachment they are eight 

 times the height of the ordinary trophoblastic ectoderm cell. 



The cytoblast cells, therefore, have already the appearance, 

 particularly in the centre of the placental area, of typical 

 placental megalokaryocytes. 



Intense proliferation is to be seen in the cells of the cytoblast 

 of the whole of this area. I have not been able to observe 

 mitotic figures, liut it must be remembered that in the case 

 of my material as well as that of Hill, fixation was not possible 

 until a couple of hours after death. 



Proliferation of the cytoblast {cyt.) and its results are shown in 

 figs. 13-^16, 19. The plasmodiblast nuclei (phji.) resulting from 

 this division are usually more darkh^ stained than the original 

 cytoblastic nuclei and for this reason are easily distinguishable, 

 particularly from the original syncytial nuclei {synji.). The 

 plasmodiblast nuclei are occasionally isolated, but more often 

 are arranged in clumps to form multinucleated masses {g.c.) 

 of sometimes large size. These resemble the giant or monster 

 cells which have been found in similar positions in connexion 

 with the placentation phenomena of higher Eutheria. 

 The main result is that the plasmodiblast makes its way into 

 the nests of syncytial nuclei, in which one or two or, in most 

 cases, a large number of these nuclei can be distinguished. 

 In such cases the syncytial nuclei have to a great extent dis- 

 appeared, the tendency being to replace them in their nests by 

 the newly-arrived foetal nuclei. 



