620 J. T. PATTERSON 
extensive area of the trophoblast is brought into close contact 
with the mucosa. Whenever the blastocyst happens to become 
anchored at the bottom of a furrow or on the side of a fold, as 
in the case of No. 316, it follows that a larger area of contact 
is possible than when its union is established on the top of a 
fold or on a perfectly smooth surface. 
Although there is an extensive area of contact in the speci- 
men under discussion, yet the place of fusion is indeed small, 
and does not occupy a space any greater than that previously 
covered by the Rauber’s layer. The chorionic vesicle rests 
upon a, mass of trophoblastic tissue which is in the form of a 
concave disc, with the concave side directed upwards, and with 
the upper margin of the disc passing insensibly into the free 
trophoblastic portion of the vesicle (fig. 31). 
The disc or primitive placenta is comparable to the attach- 
ment mass of rodents, and has been termed the Trager. In 
the armadillo the Traiger arises through the formation of the 
syncytium in Rauber’s portion of the trophoblast, followed by 
a fusion of this syncytium with the surface layer of the mucosa. 
The fused mass thus forms a bridge across which the embry- 
onic nuclei can pass from the syncytium into the maternal 
tissues, portions of which are soon destroyed by these invading 
nuclei, doubtless as a ‘result of their phagocytic or histolytic 
action. 
In specimen No. 316 the fusion is firmly established and sev- 
eral embryonic nuclei have already penetrated well into the 
mucosa epithelium (fig. 31, Hm. N.). Several other nuclei are 
on the point of passing into the mucosa. Evidences of the 
histolytic properties of these foreign nuclei are everywhere 
present in the maternal portion of the fused region, and the 
nutritive substances which result from the breaking down of the 
maternal tissues must serve as an embryotrophe. The embryo- 
trophic phase of placentation must last throughout a relatively 
long period of the early development, because neither the ma- 
ternal nor foetal circulation is established in the placenta until 
the embryonic rudiments are well formed. 
