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from their shape and structure, are found embedcled in the tro- 

 phoblast. 



Fortunately however, at a time when the two tissues are still 

 separated by the layer of flattened cells, the vacuolated tropho- 

 blast can be decisively recognised as such by its forming the 

 outer layer of the 'ecto-placental cone'. 



Taking therefore the topographical in conjunction with the 

 histological differences, I think the existence of two glycogenic 

 tissues derived from absolutely distinct sources must be admitted; 

 and if this be once granted the rest is comparatively easy. In 

 the maternal tissue all the stages in the disruption and disinte- 

 gration of the glycogen cells may be seen, in the trophoblastic 

 there is every transition from the non-vacuolated actively multi- 

 plying cells below, to the fully vacuolated cells in the upper 

 layers. This is a living tissue, that is dead; and to pretend that 

 this tissue, agreeiug in every detail with a tissue of known em- 

 bryonic origin, arises by the metamorphosis of cells which pre- 

 viously showed every sign of decay and death, would be to arrive 

 at a conclusion which I at any rate have found myself quite 

 unable to reconcile with the facts. 



Remarks on the physiology of the placenta. 



It would be idle to pretend that we have yet at our command 

 data sufficiënt to euable us to form a detail ed conception of the 

 physiology of the placenta in the proper sense of the word. But 

 I nevertheless venture to hope that some of the facts which have 

 above been set forth will serve as the foundation on which future 

 investigators may build, and so tend towards an elucidation of 

 the complicated relation effected by means of this organ between 

 the metabolism of the embryo and that of the mother at whose 

 expense the embryo is nourished. 



We may conveniently consider separately and in order the 

 nutrition of the embryo before fixation, from the time of fixation 

 until the allantoic and yolk-sac circulations are established, and, 



