THE FINAL ADJUSTMENTS 



107 



over large areas, in the cat the uterine connective 

 tissue goes, and in mice, rabbits, and men the walls 



Fig. 26. — The different types of placenta. The part derived from the 

 embryo is above, and that derived from the mother below in each 

 figure. (A) The lining of the embryonic blood-vessel. (B) Embryonic 

 connective tissue. (C) Embryonic membrane. (D) Maternal mem- 

 brane. (E) Maternal connective tissue. (F) Lining of maternal blood- 

 vessel. In (a), which is the least developed type, all six layers are 

 present. In (b), layer (C) lies against {E) in the folds. In (f), (D) has 

 disappeared entirely and (C) lies against (F). In {d) (man), (C) lies 

 against the maternal blood itself. (UM) is the uterine milk in {a) and (b) 



of the uterine blood-vessels break down and the 

 maternal blood lies right against the wall of the 

 placenta, and there are only three layers left separat- 

 ing it from the embryonic blood. In the same series 

 of animals the wall of the placenta becomes more 



