PLACENTA IN PERAMELKS 137 



embryo of (M mm. direct length, attached to the uterine 

 epithelium by a portion of the true chorion. 



In the uterus the allantoic placental area at this stage is 

 distinguishable by the fact that its surface is marked by folds 

 noticeable at once by their depth and distinctness. 



To one of these folds the foetal trophoblast is attached. 



Sections show that the uterine epithelium has become con- 

 verted by loss of cell outlines and by proliferation and migra- 

 tion of the nuclei into a syncytium as described by Hill. 



I will proceed tirst to give a description of the maternal 

 structures afterwards passing to those more concerned with the 

 eml)ryo. 



M o r p h o 1 o g y of the S y n c y t i u m . — This varies greatly 

 in character according to the locality in the uterus. Over the 

 main wall of the uterus the syncytium is thin, 0-035 mm., while 

 in the region of attachment of the trophoblast it measures as 

 near as can be judged about 0-07 mm. 



In the allantoic placental region it is that the complexity 

 of the syncytium has reached its maximum. Here, as Hill 

 has already shown and as happens over the remainder of the 

 uterus to a less degree, the nuclei of the original epithelium 

 have proliferated and migrated to the deeper portion of the 

 layer, which has now markedly thickened. The result is the 

 formation of a syncytium in which the deeplv-situated nuclei 

 assume a particular form and arrangement. These nuclei 

 ])ecome aggregated mainly in rounded njasses or nests situated 

 in lobular projections of the syncytial protoplasm. The lower 

 surface of the syncytium has a wavy appearance due to the 

 presence of these lobules. 



The syncytial nuclei at this stage are rounded with a well- 

 detined membrane, a distinct nucleolus, and indelinite chromatin 

 network which, however, is slightly more evident than it is in 

 later stages. Their lack of staining qualities makes them easily 

 distinguishable from the newly-formed trophoblastic nuclei. 

 Careful investigation of the arrangement of the epithelial nuclei 

 in each lobule shows that, when finally at rest, they are more 

 or less definitely arranged round a central cavity. This arrange- 



