84 THE BIOLOGY OF TWINS 



Dasypus, which is evidently the most highly specialized 

 genus of the Dasypodidae, the process of polyembryony 

 is the last step and has been derived from a uniparous 

 situation through the introduction of some factor that 

 causes the single blastocyst to undergo precocious 

 agamic reproduction. Polyembryony is, therefore, not 

 a primitive but a highly specialized condition, though 

 some authors refer it back to conditions in the lower 

 chordates or even to conditions in the invertebrates. 



