TWINNING IN OTHER SPECIES OF ARMADILLO 73 



to have adopted the "budding" hypothesis as an expla- 

 nation of the mode of isolation of the several embryos 

 from the ectodermic vesicle, since he uses the word 

 ''Sprossung" to describe the process. Possibly, however, 

 this term may merely imply evagination or outgrowth, 

 and thus be free from the unfortunate implication carried 

 by the word '' budding." In brief, this is Fernandez' 

 idea of the mode of polyembryonic development in 

 D. hybridus: the entire ectoderm of the individual 

 embryos originates from the undivided primary ectoder- 

 mic vesicle through a series of irregular and complicated 

 outgrowths, while the endoderm and mesoderm of each 

 embryo is produced in loco from the common mesoderm 

 at points where the outsprouting ectoderm comes in 

 contact with them. This haphazard method of origin of 

 the embryos makes it clear then why the number of 

 embryos in the Miilita is not fixed but so highly 

 variable. 



This explanation of polyembryony is purely descrip- 

 tive and implies no theory as to the factors responsible 

 for the condition. Some of Fernandez' figures of the 

 common amnion and the interrelations of the amniotic 

 connecting canals seem to indicate that not all of the 

 outgrowths of the ectodermic vesicle are primary, but 

 that some of them are secondary or even tertiary. In 

 one case (Fig. 27) there appear to be four independent 

 primary outgrowths, each connected separately with 

 the common amnion, and one compound outgrowth, 

 consisting of four branches, one of which is much 

 smaller than the rest. In another case (Fig. 30) the 

 common amnion seems to have divided into two vesicles 

 united by a narrow neck. From one half-vesicle seven 



