TWINNING IN DASYPUS NOVEMCINCTUS 37 



majority of eutherian mammals. I am strongly inclined 

 to predict that when the cleavage is made known it will 

 prove to be much Hke that of Dasyurus. This prediction 

 rests on two circumstances: first, that the history of 

 the ova of Dasyurus and that of Dasypus are alike as 

 far as we can trace them, and that the latter is unlike 



Fig. 7. — A fertilized armadillo egg with two polar bodies and the 

 male and female pronuclei side by side. 



that of other species of EutJieria; second, that the 

 arrangements of embryos in pairs and the mirror- 

 imaging effects that are so striking a feature of the 

 quadruplets are much more in accord with a type of 

 cleavage in which the blastomeres retain a regular and 

 definite position than with one in which the cleavage 

 cells shift about. 



