306 
Dr Duckworth, The histology of the 
tissues is as strongly suggested here as in the classical examples 
described by Siegenbeek van Heukelom and others. 
I am not able to adduce evidence in support of the very definite 
observations made by Frassi ( op.cit .) as to the clear communication 
between the lumina of the glands and the intervillous space. It 
must be remembered, however, that Frassi describes an early 
human embryo. In the present example of Macacus nemestrinns, 
several sections (perhaps especially No. 209) shew that the glands 
extend nearly to the intervillous space. But the glandular epi- 
thelium is in these instances degenerating, and in other cases such 
as the sections 244 (and those immediately following this), 260, 
263 — 267 (described above) and 317, the mouth of the gland 
appears to be invaded by embryonic tissues. The latter may 
very probably subsist upon the haemorrhagic contents of some of 
the glands, as suggested by Frassi. The latter author suggests 
that the presence of leucocytes provides a good criterion of 
maternal tissues as contrasted with those of embryonic origin, but 
my observations lend little support to this, though I prefer not to 
lay stress upon the subject till I have carefully revised the prepa- 
rations here described. 
(3) (c) The nature of the embryonic cells concerned in 
the preceding descriptions, 3 (a) and 3 ( b ). 
The embryonic cells which come into relation with the 
maternal capillary vessels and glands, are so far as can be 
judged, continuous with those of the villous processes. It is 
hard to find in the distinctly maternal tissues any isolated masses 
of cells which can be pronounced unhesitatingly to be embryonic 
intruders, though cell-groups of suspicious appearance occur. 
Of the villous processes, some are short and project freely into 
the intervillous spaces. Others are longer, and their “ maternal ” 
extremities are not free but appear as though expanded laterally 
so far as to fuse with each other. From this fusion results the 
mass of embryonic tissues which is in immediate relation with the 
uterine wall. Siegenbeek van Heukelom (supported by Hubrecht 
and Peters) has suggested another explanation of these appear- 
ances. He supposes that the intervillous spaces are not situated 
between processes which originally projected as villi from the 
blastocyst. But instead, he offers the explanation that the inter- 
villous spaces really arise as clefts in a continuous mass of 
thickened trophoblast. Whichever view may be correct cannot 
be decided by the specimen now described, but in any case we 
must distinguish the shorter indubitable villi projecting into (and 
ending in) the intervillous spaces, from the longer, larger processes 
which form the boundaries of those spaces ; the latter are the 
“ balken ” described by Siegenbeek van Heukelom, and in fact 
