TWINNING IN DASYPUS NOVEMCINCTUS 6i 



but accurate in so far as the relation of placenta and 

 membranes is concerned. The view is one that would 

 be obtained if one looked into the vesicle from its lower 

 transparent end; the eye sees the. embryos head-on, 

 so to speak. The axes (dorsoventral and bilateral) 

 are the same as those of the mother. 



In full-term eggs the placental complex consists of 

 two well-defined areas corresponding to the right and 

 left sides of the uterus. Those two heavily villous 

 areas {p' and p") are separated, dorsally and ventrally, 

 respectively, by narrow non-villous areas {dnv and vnv); 

 these serve as points of demarkation between the right 

 and left placental regions; they are not always precisely 

 mid-dorsal and mid-ventral, but usually slightly asym- 

 metrical. Frequently placental blood vessels run across 

 the non-villous area so as to connect the circulation of 

 the two sides. A single fetus may have parts of its 

 placental material in both of the bilateral placental 

 areas. It appears then that the double placenta is 

 merely a mechanical adjustment of the fetal membranes 

 to the bilateral blood supply of the uterus. 



Although one fetus appears to belong to the right 

 quadrant, another to the left, a third to the dorsal, 

 and a fourth to the ventral, it is obvious that, so far 

 as placental connections are concerned, one pair (I and 

 II) belongs to the left side, the other pair (III and IV) 

 belongs to the right. 



The umbilicus of each fetus is close to an amniotic 

 partition composed of the right-hand side of its own 

 amnion and the left-hand side of the amnion of its right- 

 hand neighbor. Curiously enough there has been a 

 crowding to the left on the part of each amnion until 



