CHAPTER II 



TWINNING (POLYEMBRYONY) IN THE ARMADILLO, 



DASYPUS NOVEMCINCTUS 

 HISTORICAL 



Polyembryony^ is exhibited by two closely allied 

 species of armadillo belonging to the genus Dasypus^ 

 {Tatusia or Tatu of some writers), D. novemcinctus 

 and D. hyhridus. Certain significant facts have been 

 known about the latter species for about thirty years. 

 H. von Jh'ering in 1885 and in 1886 published two brief 

 notes in which he stated that he had secured two preg- 

 nant females of this species, the uterus of each of which 

 contained eight fetuses, all inclosed within a single 

 chorion. All in both sets were males. On the basis 

 of this observation he published in a subsequent note 

 the suggestion that all of the embryos of each set were 

 a product of the splitting of a single fertihzed egg into 

 a number of separate embryonic primordia. Although 

 the bearings of this situation on important problems 

 of sex-determination and heredity were not appreciated 

 by von Jhering, it must be acknowledged that, by a 

 flash of insight, he arrived at an entirely correct diagnosis 

 of the underlying biological significance of the observed 

 conditions. 



^ Polyembryony is a unique mode of twinning in which plural 

 offspring are derived from a single fertilized egg. 



^ Although most writers who have dealt with this species have 

 given it the generic name Tatusia, the laws of priority favor the generic 

 name Das y pus. 



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