54 



THE BIOLOGY OF TWINS 



top and the common amnion at the bottom of the figure. 

 This arrangement, doubtless, looks upside down to one 

 famihar with previous accounts of the embryology of 



Fig. 17. — ^Armadillo egg with quadruplet embryos attached to 

 primitive placenta, which is a bowl-shaped area at top of figure. Note 

 the connecting canals running downward to the original common point 

 of origin, which is now occupied by the small common amnion. (See 

 stage IX.) (Redrawn from Newman and Patterson.) 



Dasypus, but the reversal of axis is an important feature 

 of the embryonic history and must be indicated just 

 as it appears. The comparatively smooth outline of 

 the Trager region is due to the fact that the period of 



