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 Trager 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, Em. 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. 



