PLACENTA IN PERAMELES 



161 



of maternal cellular material. Haematids are often to be found 

 contained in the plasmodium in process of being absorbed. 



Glands . — Most of the glands of the allantoic placental 

 area have undergone certain characteristic changes. Instead 

 of being narrow and tortuous, they have now become generally 

 straighter and wider. 



The necks of the glands are particularly spacious, and often 

 the gland on its entrance into the diploplasma shows a barrel- 

 like enlargement. The aperture of the gland in the placental 

 area is closed by the cytoblast, while the plasmodiblast has 

 disappeared from its mouth but bounds this portion of the gland 

 on either side where it has been responsible for the disorganiza- 

 tion of the gland epithelial cells (fig. 28) . The cells of the body and 

 neck of the glands have now been transformed into a low cubical 

 epithelium, and their nuclei instead of being oval are rounded. 

 The gland-cells throughout are ciliated. Occasionally some of 

 the glands swell to a relatively enormous size. A further 

 feature of note is that a number of glands have penetrated 

 into the muscularis. 



The Allantois . — For the general description of this 

 I would refer the reader to Hill's account. At this stage the 

 splanchnic mesoderm of the allantois is found fused with that 

 of the chorion over the full extent of the placental area. 

 There is but a small amount of penetration of allantoic tissue 

 into the plasmodiblast, and this only becomes possible where 

 gaps have occurred in the disorganized cytoblast. The complex 

 ' interlocking system ' — by which apt phrase Hill describes 

 the mutual apposition of foetal and maternal capillaries — is 

 brought about by short finger-like downgrowths of the allan- 

 toic mesoderm combined with the opposite (inward) tendency 

 of the maternal capillaries. This mutual process becomes more 

 and more easy the more the basal cytoblastic layer loses its 

 integrity and becomes converted into plasmodiblast. Where the 

 cytoblast remains practically intact as at the margins (fig. 23), 

 the approximation of foetal and maternal vessels does not 

 occur. The maximum penetration of the allantois appears 

 to be a little more than the thickness of the cytoblast. One 



NO. 265 M 



