TWINNING IN DASYPUS NOVEMCINCTUS 47 



that the embryo though inside out is clearly polarized 

 and bilateral and that it is still one embryo. A further 

 evidence of bilaterality is, seen in the mesoderm {ms) 



Tra 



'""dtr 



Fig. 13. — ^An armadillo egg showing first division into a double 

 individual. The two first embryos (II and IV) are shown as right and 

 left outgrowths of the ectodermic vesicle. (For details see description 

 under stage VI. Lettering as in Fig. 12.) (Modified from Patterson.) 



which is proliferating at two bilateral points where the 

 ectoderm and the endoderm part company. 



Stage VI. The first step in twinning — the primary 

 embryos (Fig. 13). — The ectodermic vesicle, which was 



