146 T. THOMSON FLYNN 



It is evident enough that in all cases of placentation where 

 the uterine epithelium is not immediately destroyed, the area 

 of fixation consists for a longer or shorter time of a conjoint 

 layer of foetal and maternal epithelia, each having the charac- 

 teristics outlined above. Development of tlie former and 

 degeneration of the latter proceed in Perameles side by 

 side, and it would be convenient if a single expression could 

 be coined to denote the composite layer consisting of the 

 two. No convenient term seems to exist, and I propose to 

 use the name ' diploplasma ' to indicate the conjoint layer 

 consisting of foetal chorionic ectoderm and maternal tropho- 

 spongia. 



The diploplasma consists in Perameles of three zones. 

 Along the line of junction of foetal and maternal tissues, the 

 syncytium is undergoing degeneration and resorption by the 

 Plasmodium. Such a degenerating syncytium is called a 

 symplasma (Schoenfeld, 1903), a term which can be correctly 

 applied only to maternal structures of a degenerate nature 

 contained in the plasmodium. Eecently, however, Willey 

 has suggested its use to indicate the junctional portion where 

 there is an intimate mixture of active foetal elements and 

 degenerating maternal material. 



Accepting this suggestion (Willey, 1914), the three zones of 

 the diploplasma in Perameles consist of the following : 

 a middle junctional layer composed of mixed foeto-maternal 

 tissue (symplasma) with, on one side, a pure layer of foetal, 

 and on the other side, pure maternal material. 



The foetal portion differentiates early into a basal layer, 

 the cytoblast, and a plasmodial layer, the plasmodiblast. 

 Contrary to what has been stated by Willey for other mammals, 

 the cytoblastic layer in Perameles is well in evidence before 

 the time of attachment of the allantois. 



The plasmodiblast has a twofold duty concerned with 

 (a) attachment, (h) nutrition. Both functions are performed 

 with the aid of root-like pseudopodial processes which attack 

 the maternal elements converting them into symplasmatic 

 debris which is ingested. Such nutritional material is passed 



