TWINNING IN OTHER SPECIES OF ARMADILLO 69 



larger though much less definitely fixed. There 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, novemcincius (Figs. 12 and 14) they should 

 be viewed inverted. Note Trager cavity {trcav), trophoderm plate 

 {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 variabiUty 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 

 abnormahty, owing to overcrowding and ill-success in 



