20 RICHARD ASSHETON AND THOMAS G. STEVENS. 
nigrosin, and deeply with saffranin; it is not affected by 
osmic acid nor by ferrocyanide of potassium, whereas the 
mesoblastic portions of the terminations of the foetal villi are 
stained an intense blue. 
With fuchsin and orange there is a slight differentiation 
between the outer thinner and inner thicker layers, which are 
further distinguishable by the presence of the rounded cells 
in the outer layer and the elongated nuclei in the inner layer 
(fig. 23). 
It seems probable, therefore, that it is of double origin, 
partly from foetal trophoblast (the inner thicker portion) and 
partly from maternal tissues (the outer thinner), in which 
case the large rounded cells with small nuclei would be of 
maternal origin. 
It is difficult to understand what the function of this layer 
may be, unless it is to prevent for the moment—for some not 
discernible reason—the entrance of the fcetal villi into the 
maternal tissues. The fact that cells are being budded off 
from the trophoblast seems to indicate a non-absorbent epi- 
thelium; that the nuclei of these budded-off cells should die 
and disappear shows it is not a phagocytic edge that is being 
formed, and this is also rendered improbable by the smooth 
regularity of its superficies. The ready response to the iron 
test noticed above suggests the absorption of iron from this 
layer. We have searched in vain, however, for blood 
remains, which, perhaps, one might expect to find if this 
layer was the seat of destruction of hemoglobin-bearing 
corpuscles. | 
A glance at the cut end of Owen’s specimen (fig. 15) will 
show that the surface of the section is roughly marked out 
into areas by the longer and stouter branches of the fcetal 
villi. Within the boundaries of each such area we find on 
the whole a uniform stage of development, but one area will 
often show a different state to its neighbours, and roughly 
speaking the nearer the area is to the maternal surface and 
to the edge of the placental zone the earlier is the stage 
represented. 
