304 
Dr Duckworth, The histology of the 
On the embryonic side, the villous processes have united to 
some extent, forming an irregular plateau of ectoblast (trophoblast) 
like that described by Siegenbeek van Heukelom {op. cit.) in the 
human ovum. These embryonic villous processes can be traced 
far into the “ placentar-polster ” and in some sections (cf. Figs. 7 — 
11) embryonic tissues invade dilated maternal capillary vessels, 
and also maternal glands, as will be described in the sequel. 
(3) (a) The mode of communication whereby the maternal blood 
passes from the uterine capillaries to the intervillous spaces. 
As one traces the sections serially from the periphery inwards, 
evidence is soon obtained of the passage of red-blood corpuscles 
into the interstices of the stroma cells. This is represented in 
Fig. 5 which shews the conditions observed in the 134th section. 
In this section some dilation of the uterine capillaries can be seen 
and the dilation is more evident as the centre of the area of 
attachment is approached. Fig. 6 representing section 266 serves 
to illustrate this point. Thus red-blood corpuscles may reach 
the intervillous spaces after a longer or shorter course, but 
where only a few escape at a time and wander among uterine and 
embryonic cells, it is by no means improbable that they run the 
risk of destruction before the villi are reached. The appearances 
observed under a higher power than that employed for the repre- 
sentations in Figs. 5 and 6, are seen in Figs. 7 and 8 (taken from 
sections 266 and 274). 
In each of the latter, a capillary vessel is shewn stretching 
across the figure and the blood stream divides to embrace with 
two side-channels a mass of tissue which I submit to be almost 
wholly embryonic in origin. 
The endothelial cells lining the capillary vessel are traceable 
up to a certain point only. Beyond this they are lost and the 
blood thenceforward bathes the embryonic tissues directly. The 
blood thus travels to the intervillous spaces, which must therefore 
be regarded as bounded by embryonic cells. Upon this subject 
very different opinions have been expressed. Strahl in Hertwig’s 
Handbuch, Vol. n., pp. 337, 338, distinguishes five distinct 
views. The present description accords most closely with that 
placed third in the list by Strahl and held by such authors as 
Farre, Kolliker, Langhans and Heinz. To these, the name of 
Siegenbeek van Heukelom may be added. 
There is no evidence of proliferation of the endothelial cells to 
provide a lining for the intervillous spaces. 
As to the mode of destruction of the capillary wall, one must 
be guarded. Externally the stroma soon becomes less dense, the 
constituent cells become more widely separated as the limits of 
