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certain granular débris. Further it has been shown that tbe outer 

 layer of tropboblast becomes also couverted iuto a glycogenic 

 tissue, differiug from the similarly raodified maternal cells not 

 only iu bistological characters, but also in the fact that glyco- 

 genesis only sets in here when the maternal tissue has passed 

 the maximum of its development and is beginning to show the 

 first signs of degeneration, at a time too when the delimiting 

 layer of flattenecl cells is still present. 



In this tissue the vacuolation steadily proceeds, while in the 

 deeper layers which are not at present vacuolated, nuclear divi- 

 sion and active growth still continue; and finally an enormous 

 mass of glycogenic tissue is produced which gradually encroaches 

 upon, and occupies the space now deserted by the degenerate 

 maternal cells. In this way there is formed, on the extreme 

 maternal side of the placenta, a complex tissue of doublé origiu, 

 namely maternal arteries and supporting cells embedded in a 

 glycogenic tissue derived from the tropboblast. 



These facts of themselves appear to me to lend considerable 

 support to my view without laying too much stress on the histo- 

 logical differences, in the character of the vacuolation, the shape 

 of the cells, and the structure of tbe nuclei, which have been 

 shown to exist between the two tissues. At the same time, taking 

 into account the difficulty of the subject, the possibility of other 

 interpretations must not be ignored. For example, the bistological 

 differences might be overlooked; it might be urged that there is 

 only one kind of glycogen cell, and that the glycogenic tissue 

 found in later stages is made up by the union of the loose 

 cells of an earlier stage, which regain the power of division. It 

 must be admitted that though in the very great majority of cases 

 the difference in structure between the two sets of cells is really 

 striking, it is still possible to find maternal cells with, perhaps, 

 two nucleoli, instead of the characteristic single one, in the 

 nucleus, or with irregular vacuoles; and the difficulty of making 

 the structure the ultimate criterion of a real difference is, of 

 course, only increased when maternal cells, as I interpret them 



