TWINNING IN OTHER SPECIES OF ARMADILLO 69 



larger though much less definitely fixed. Hicre is a 

 strong tendency, however, for the species to settle down 

 upon the number eight, though litters of nine are fre- 

 quent and from seven to twelve are reported. 



Fig. 23 



Figs. 23 and 24. — Diagrammatic views of two stages in the develop- 

 mant of Dasypus hybridus (the Mulita armadillo). For comparison 

 with equivalent stages of D. novemcinctus (Figs. 12 and 14) they should 

 be viewed inverted. Note Trager cavity (trcav), trophoderm jilate 

 (tr pi), ectoderm (ec), endoderm (en), mesoderm (ms), diplotrophoblast 

 (dtr), extra-embryonic cavity {ex c), uterine mucosa {mucut), common 

 amnion {c am), primitive streak of embryos {pr st), amniotic connecting 

 canal {en am). (From Fernandez.) 



The fact that there is so much variability in the 

 number of polyembryonic offspring in this species 

 apparently indicates that the condition is of com- 

 paratively recent origin. This view is supported by 

 the fact that so large a percentage of embryos in 

 advanced stages are dead or show signs of marked 

 abnormality, owing to overcrowding and ill-success in 



