LAYER OF LARGE FREE CELLS 
21 
It will be convenient at this point to consider the origin of the large 
cells which are seen lying free in the blood space within the necrotic 
layer of the decidua. These cells closely resemble bodies which are 
certainly cross sections of plasmodial strands, but when traced through the 
sections it becomes quite certain that they are not continuous with the 
plasmodium, but are really isolated cells. Plate vi, Fig. 6, shows them 
at a point where they form almost a continuous layer for a con¬ 
siderable extent. The necrotic zone of the decidua is depicted. The 
inner edge of the dead or dying tissue is extremely irregular and is 
excavated into bays, many of which include one or more of the cells 
under consideration. Within the layer itself are seen spaces inclosing 
cells in different phases of degeneration. The nuclei are identical with 
those of the completel} 7 free cells, and the protoplasm stains the same 
dusky-red in both cases. There are two ways of interpreting these 
appearances. 
(1) The cells within the spaces in the necrotic tissue may be foetal, 
i.e. trophoblastic, derivatives which, having wandered outwards, are here 
caught in the act of attacking the necrotic wall of the implantation 
space and so causing its gradual enlargement. • 
(2) The cells may belong to the decidua itself, and are being set 
free from the necrotic zone as it is absorbed and the implantation 
cavity is enlarged. 
The following considerations are in favour of the latter alternative : 
(1) The cells cannot be cross sections of plasmodial strands because 
they cannot be traced back into the general plasmodial meshwork. 
(2) The outer shell of trophoblast is entirely plasmodial. No cells 
which can be definitely identified as embryonic, occur anywhere except in 
that part of the wall of the blastocyst which we have called the cyto- 
trophoblast. 
(3) The cells, both in the character of the nuclei and reactions of the 
protoplasm, agree with cells further out in the decidua, which are clearly 
degenerating maternal cells, and are distinguishable from the trophoblast 
in both these respects. They are quite different from the wandering tropho¬ 
blast cells of later phases. 
