STUDIES IN MAMMALIAN EMBRYOLOGY. 501 



The simultaneous change in the maternal proliferated epithe- 

 lium is this, that the sharply defined surface demarcation of the 

 layer tends to disappear, that the cell boundaries between the 

 cells of the superficial layers become less distinct, that the 

 nuclei stain more deeply, lose their sharp outline, and take the 

 aspect of spherical drops of nuclear matter in which the minute 

 details (nucleolus, granula, &c.) of ordinary nuclei can no 

 longer be detected. These changes, both in protoplasm and 

 nuclei, cause this part of the maternal tissue to be so exceed- 

 ingly like the adherent embryonic cell matter, that very soon 

 a distinction between the two becomes more difficult and even 

 impossible. 



A most effectual adhesion of the two tissues has now come 

 about ; they may be said to be fused together. Especially in 

 the stage of fig. 5 (uterus, No. 73) the cementing process 

 between trophoblast and mucosa is very perfect, and in many 

 of the blastocysts secondary changes in the tissues of the belt- 

 shaped region of attachment have not yet commenced. Where 

 these are initiated they have the character of a granular de- 

 generation, as indicated in the lower part of fig. 51. In the 

 upper portion the fused parts have a yet more uniform aspect. 



A more detailed and at the same time comparative inspec- 

 tion shows that this granular degeneration aff'ects both the 

 maternal and the trophoblast cells. In how far it is preparatory 

 to vasifactive processes in this region cannot exactly be made 

 out, maternal blood penetrating into capillary spaces in this 

 zone of fusion independently of any preceding granular trans- 

 formation. 



Amongst the six blastocysts of uterus No. 73 there was one 

 yet partially protected by its zona pellucida; this is undoubtedly 

 abnormal for this stage, and a few other peculiarities in its de- 

 velopment seem to confirm this view. As such I may mention 

 partial and local proliferations and thickenings in the tropho- 

 blast instead of the flat application and parallel fusion against 

 the mucosa. 



The stages represented by the uteri 45, 43, and 51 will be 

 discussed together. In all of them the fusion has become yet 



