early placenta of Macacus nemestrinus. 305 
the definitely uterine tissue are approached. The continuity 
of the lining of the capillary tube is broken even before the 
endothelial cells finally disappear, and red-blood corpuscles are 
found outside the tube (see especially in Fig. 7) and in the inter- 
stices of the uterine cells. 
Peripherally, the embryonic tissues appear to invade the 
capillary vessel, perhaps even to press its wall inwards before 
destroying its continuity. But the embryonic cells are themselves 
liable to suffer from this contact. The frayed-out appearance 
of the tissue attached to the embryonic mass in Fig. 8 especially 
(“/”) indicates that some sort of conflict has taken place. 
Isolated strips of such frayed-out material within some of the 
capillary vessels suggest the invasion of the latter by detached 
masses of embryonic origin. Such an invasion has been definitely 
described by Siegenbeek van Heukelom (for the human ovum), 
but the appearances in the present instance do not warrant an 
equal definiteness in description. 
(3) (b) The relation of the embryonic tissues to the uterine 
glands, is shewn in Figs. 9, 10, 11. These represent three sections 
(viz. Nos. 263, 265, 267) in which a mass of embryonic cells was 
observed invading a tubular gland into which haemorrhage had 
taken place. The lining epithelium of the gland has disappeared 
and it is hard to recognise with certainty even degenerating 
remnants of the epithelial cells. Around the gland, as its mouth 
is approached, the uterine stroma becomes less dense, and the 
open mesh-work thus produced resembles that surrounding the 
capillary vessels at their peripheral ends. 
My interpretation of Figs. 9, 10, 11 is that a rounded mass of 
embryonic cells has approached the peripheral end of the gland 
obliquely. As this approach progresses, the tissue becomes 
rarefied in density. Destruction of the uterine stroma cells is 
thus strongly suggested, but whether the active agents in this 
destruction are cells, or enzyme-like fluids produced by the 
embryonic or other tissues, it is not possible to say. Leucocytes 
are not abundant, and of such as are seen, the majority are 
characterised by the peculiar division of the nuclei into tetrads, 
similar to those seen by Selenka*, and Siegenbeek van 
Heukelom j*. Some of these remarkable cells are found, as shewn 
in Figs. 10 and 11, in the closest relation to or even within 
the embryonic tissues. The appearances thus indicate a process 
of invasion wherein the embryonic cells play an active part. 
The process resembles that already seen in connexion with 
the capillary vessels, so that the activity of the embryonic 
* Studien, 8tes Heft, Taf. n. Fig. e, “ l. ” 
t Arcliiv filr Anatomic, 1898, Taf. i. 
