TWINNING IN OTHER SPECIES OF ARMADILLO 75 



Fig. 29 



dition that occasionally appears in which three fetuses 

 are alike and one 

 quite different. 



A striking feature 

 of Fernandez' collec- 

 tion of the eggs of 

 D. hybridus has to do 

 with the frequent, 

 almost universal, 

 occurrence of one or 

 more degenerate 

 embryos in an egg. 

 These embryos may 

 be the victims of 

 severe competition 

 for placental surface, 

 or they may be the 

 result of outgrowths 

 produced from un- 

 favorable regions 

 of. the ectodermic 

 vesicle. The portion 

 of an egg shown in 

 Fig. 31 indicates 

 that ectodermal out- 

 growths may fail to 

 reach the walls of the 

 egg and, through lack 



Fig. 30 



Figs. 29 and 30. Two more views of 



conditions like those shown in Fig. 28. 



There are in the upper figure 13 embryos, 



each with a connecting canal; A, B, and 



C are evidently rudimentary or aborted 



embryos. In the lower figure all of the 



of endodermic and . successful embryos (1-7) seem to have 



mesodermic elements, '^°^^ ^^°'^ one-half of the ectodermic 



^, r ^^ ^ ^ vesicle and only a rudimentary embryo 



may thus fail to be- ^g^ ^^^^ ^^^ ^^^^^ ^^^^ ^^^^^^ 



come complete em- Fernandez.) 



