102 A. A. W. HUBRECHT. 
in figs. 12—16, the lateral attachment of these early and 
much younger blastocysts is seen to have come about in the 
same spots where afterwards the reniform placenta will develop. 
The attachment of the early blastocyst, long before any allan- 
tois or allantoidean circulation has made its appearance, comes 
about by means of a very considerable proliferation of the 
trophoblast. The proliferating patches of trophoblast are 
double, and face the two spots in the uterine wall alluded to. 
It is beyond all doubt that even before this proliferation of the 
embryonic trophoblast has commenced the maternal tissue has 
become visibly modified in those four regions of the mucosa 
which correspond to the future placentary region, i.e. the right 
and left inner surface of the uterus-horn when cut transversely. 
The tubular uterine glands are then more particularly 
limited to the mesometrical and antimesometrical regions of 
the lumen; on the spots in question the interglandular con- 
nective tissue has proliferated with partial displacement and 
partial obliteration of the glands there situated. 
The uterine epithelium does not take part in this growth. 
It is, on the contrary, destroyed by the trophoblastic prolifera- 
tion as soon as the blastocyst commences to adhere. This 
trophoblastic neoformation is then gradually vascularized 
(maternal blood penetrating into it), and undergoes a series of 
interesting but complicated histological transformations. In 
a future paper I propose to treat this placentation process of 
Tupaja more fully; it may here suffice to remark that against 
these early placentary cushions the yolk circulation is first 
applied, and that in further stages of pregnancy the yolk-sac 
is again removed from thence and replaced by the allantoidean 
blood-vessels which then constitute the definite double placenta. 
The placentas are shed at birth as are those of Sorex and 
Erinaceus ; they are not resorbed in situ as is that of Talpa.! 
The fully ripe placentas, shortly before birth, are in Tupaja 
connected with the maternal tissue by an area which all along 
its outer circumference is most easily detached and very loosely 
connected. ‘Towards the centre, where the principal blood- 
1 Cf. ‘Quart. Journ. Mier, Sci.,’ vol. xxx, p, 346, 
