Anatomy. — ''The Involution of the Placenta in the Mouse after 

 the Death of the Embrj/o'\ Bj Dr. A. B. Droogleever 

 FoRTUYN. (Communicated by Prof. J. Boeke). 



(Communicated in the meeting of June 29, 1918). 



In various species of mammals which are pregnant with several 

 embryos at the same time it accidentally occurs that one or more 

 embryos die before birth. The subsequent fate of the placenta has 

 been controlled in only a few cases and it appears to be intimately 

 connected with the structure of the placenta. Noav this structure in 

 the mouse considerably deviates from that in many other mammals. 

 So it seemed to be w^orth while to investigate in this animal too, 

 as has not yet been done, the involution of the placenta after 

 interruption of the pregnancy. For this purpose the uteri of 8 mice 

 were at my disposal containing together besides many normal egg- 

 chambers 20 egg-chambers without an embryo. Judging from the 

 degree of development of the normal egg-chambers one of the 8 

 mice had been killed on the 13^1' day of the pregnancy, one on the 

 15^1', four on the 16^'\ one on the 17'^i and one on the 18^11 day. 



The 20 empty egg-chambers are more fully described in a paper that 

 I offered to the "Tijdschrift der Nederlandsche Dierkundige Vereeni- 

 ging". Here I shall only communicate the results in a general way. 



Never was any other trace of the embryo left than some free 

 cells which could not be duly recognised. Many portions of the 

 foetal membranes survived the embryo, but they did not all do so 

 during the same time. So among the empty egg-chambers some 

 groups could be recognised with more or less remainders of the 

 foetal membranes. 



In the first group the giant-cells (in the mouse trophoblastic ^cells 

 which are greatly enlarged and have become independent) and the 

 membrane of Reicheht were left and moreover parts of the ecto- 

 placental cone and of the proximal or distal entoderm of the yolk-sac 

 or of both. The proximal entoderm of the yolk-sac could be 

 well recognised by the appearance of the cells, but it had 

 always been broken into pieces. The distal entoderm of the 

 yolk-sac sometimes lined large pieces of the membrane of Reichert 

 internally; besides free cells of it occurred. The ectoplacental cone 



