618 J. T. PATTERSON 
Particularly is this true of the changes which immediately follow 
the attachment of the blastocyst. It is therefore proposed 
briefly to describe some of those changes involved in the early 
history of implantation and placentation which are essential 
to a clear understanding of the embryology of the armadillo. 
This account has been deferred until now, because it will be 
somewhat easier to follow after the description of the develop- 
ment has been read. 
A statement as to the manner in which the embryonic vesi- 
cle migrates along the horizontal groove of the uterus and even- 
tually attaches itself has been given above. The principal 
facts are as follows: After the blastocyst has reached the placen- 
tal area, which lies at the extreme anterior tip of the fundus, 
it adheres to the mucosa,-apparently for some time before the 
actual placentation or intimate union with the uterine mem- 
brane is consumated. Four clear and two somewhat doubtful 
cases of early adhesion between the ovum and the mucosa have 
been observed. In every instance the ovum freed itself either 
immediately or very shortly after the application of the fixing 
fluid, thus indicating that the implantation proper had not 
really taken place. Fortunately, these vesicles were studied in 
salt solution under the binocular microscope before fixation and 
it was possible to make out several important points. It was 
observed that the ovum always comes to rest upon the uterine 
surface in such a way that the embryonic spot or germinal area 
is turned toward the mucosa. Hence, the foetal contribution 
to the early placenta arises from that portion of the trophoblast 
which overlies the inner cell-mass; that is, from the so-called 
Rauber’s layer. 
It is to this region of the trophoblast then that one must look 
to detect the first indications of placentation. In five of the 
blastocysts to which we have just called attention no evidence 
of importance in this connection was observable, but in the sixth 
unmistakable indications of early placentation are present. In 
this specimen Rauber’s layer is seen to have undergone impor- 
tant modifications. Several of the cells are in mitosis, and all 
of the cells of this region have lost their original attenuated 
