early placenta of Macacus nemestrinus. 301 
blood passes from the uterine capillary vessels to the intervillous 
spaces. 
(&)* The relation of the embryonic tissues to the uterine 
glands. 
(c)f The nature of the embryonic cells involved in the 
preceding processes (a) and (6). 
(1) The implantation of the blastocyst in the uterine wall. 
The first point to notice is that the blastocyst is implanted 
upon the uterine surface without having sunk into the substance 
of the uterine wall. The blastocyst is not received into a crypt or 
an enlarged glandular orifice. Herein, the present specimen 
corroborates the observations of Selenka upon the blastocysts 
(in similar early stages) of Semnopithecus (pruinosus and nasicus), 
so that these primate forms differ from man. In the latter, the 
observations of Peters {op. cit.) shew that the blastocyst does not 
remain upon the surface. In Macacus nemestrinus and the Semno- 
pitheci, a primary placenta is formed at the first site of attachment, 
but as the blastocyst expands, it comes into contact at its opposite 
pole with the opposed wall of the uterus, and here a secondary 
placenta is formed. In this way the twin placental discs of these 
monkeys arise. As regards the details of this process, it appears 
to me justifiable to presume that in the present specimen the 
extent of the primary attachment is less than it will subsequently 
become. And therefore it can be inferred that if the sections are 
studied serially, the events occurring in the more peripheral 
sections will successively reproduce those which took place while 
the more central parts of the blastocyst were contracting the 
relations they now bear to the maternal tissues^. 
* Siegenbeek van Heukelom ( Archiv fur Anatomie und Physiologic, Anat. 
Theil, 1898, p. 12) describes with some minuteness the conditions of the uterine 
glands at a very early stage in the formation of the human placenta. No traces of 
degeneration in the glandular epithelium were seen. Nor was there evidence of the 
transformation of such epithelium into a syncytial mass. Some glands contained 
blood and this was regarded by Siegenbeek van Heukelom as suggestive of patho- 
logical change. But the occurrence in a wild animal (in its natural surroundings) 
such as that which furnished the present specimen, indicates that haemorrhagic 
invasion of the glands may occur in any case, and to this view Siegenbeek van 
Heukelom evidently inclines [op. cit. p. 12). 
The same writer declares that the epithelium of the uterine glands disappears, 
and takes no important part in the process of placental formation. 
+ An excellent resume of the literature relating to the nature of the embryonic 
cells involved in early placental formation is provided by Strahl in Hertwig’s 
Handbuch, pp. 337 et seq. Robinson’s lectures may also be mentioned, as well as 
Voigt’s instructive papers (for reference to which v. infra). 
J The allowance to be made for the flattening out of the previously spherical 
blastocyst in the processes of fixing, hardening, embedding and cutting lias not 
been overlooked. 
