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phoblastic) villi then penetrated a spongy layer of maternal origin 

 which was copiously supplied with capillary blood vessels. The 

 cells on the outer border of this spongy layer were of a consider- 

 able size. Outside this again was a sheet of flattened decidual cells. 



Later the ectodermal villi are in their turn penetrated by the 

 capillaries of the allantois, which are brought into closer relation 

 with the maternal circulation by the disappearance of the endo- 

 thelium from the blood vessels in the sub-chorionic and nriddle- 

 layers of the placenta. The cells lining the maternal channels in 

 these regions unite to form a plasmodium. 



Later still the adjacent maternal and fbetal blood spaces take 

 on a radial arrangement. The maternal blood is brought to the 

 placenta by a single artery, which passes straight through to the 

 embryonic side. Thence the blood ascends through the placenta 

 into a system of venous lacunae which form the upper bouudary 

 of the organ. 



Frommel has also described certain curious 'Epithel-strange' in 

 the middle region of the placenta, but whether he means these 

 to be derived from the uterine epithelium, or the deep-ends of 

 the ectodermal villi is not clear. According to him they are the 

 seat of blood formation ; 'die mittlere Schicht der Placenta von 

 'Myotus murinus ist ein mütterliches Blutbildungsorgan'. 



Nolf has been able to add a good deal, in certain respects, to 

 Frommel's account, to correct it in others. 



He has shown that Frommel's spongy layer, in which the 

 superficial capillaries are embedded, is in reality a plasmodiblast. 

 As Frommel also said, the endothelium of these superficial capil- 

 laries subsequently disintegrates. He has confirmed van Beneden's 

 account of the disappearance of the uterine epithelium, and has 

 described a process, comparable to what occurs in many forms, 

 of intense interglandular proliferation of subepithelial tissue prior 

 to the attachment of the blastocyst. 



This proliferation gives rise to a 'couche paraplacentaire', forming 

 the outer border of the placenta. Two points of interest in con- 

 nection with this layer may be mentioned. Firstly its outermost 



