EMBRYONIC RECONSTITUTIONS 539 



of many of these forms from a single egg or an originally single embryo.^'' 

 Evidently such duplications are results of an agamic reproduction — a bud- 

 ding or fission with reconstitution of pattern — occurring in early embry- 

 onic stages; but conditions concerned in their origins can usually only be 

 inferred or guessed at. 



Experiments, both on embryonic and postembryonic stages of plants 

 and animals, show that decrease of dominance by exposure to inhibiting 

 conditions may result in a greater or less degree of physiological isolation 

 of previously subordinate parts, in establishment of new dominant re- 

 gions, and, in some forms, with proper experimental procedure, in com- 

 plete obliteration of the original polarity and dominance. That somewhat 

 similar factors are concerned in many cases of nonexperimental embryonic 

 duplication, even in higher vertebrates, seems probable, as suggested by 

 Newman (1917^^, 1923). Toxic or other conditions inhibiting developmen- 

 tal activity may weaken dominance and polarity to such an extent that 

 new polarities and dominant regions may arise in less susceptible regions 

 or after the inhibiting conditions cease to act, either in relation to what 

 remains of the original pattern or in reaction to local differentials. The 

 high frequency of duplications with definite relation to the original sym- 

 metry pattern suggests that this often plays a part in determining locali- 

 zation of the new dominant regions. Partial axial duplication may, of 

 course, also result from mechanical division of a dominant region — for 

 example, split tails, limb buds, etc. Accidental or pathological conditions 

 may determine some duplications in this way. 



Even among the mammals, however, polyembryony is not Hmited to 

 teratological forms and occasional identical twins. In two species of arma- 

 dillo development is normally poly embryonic. With few exceptions four 

 embryos develop from a single egg in the nine-banded armadillo, Dasypus 

 {=Tatusia) novemcinctus,^^ and from six to twelve, usually eight or nine, 

 in D. hyhridus (Fernandez, 1909). The quadruplets of D. novemcinctus 

 arise by two successive agamic reconstitutions of two embryonic primordia 

 from a single one. According to Patterson, these are primary and second- 

 ary buddings, but Newman regards them as fissions. Since they involve 

 the origin of new axiate patterns, they seem to resemble buds more closely 

 than fissions. The new patterns apparently originate in definite relation 



'3 See, e.g., Klaussner, 1890; Dareste, 1891; Bateson, 1894; H. H. Wilder, 1904, 1908; 

 Schwalbe, 1907; Gemmill, 1912; Newman, 1917(7, 1923; and citations by these authors. 



^■^ Newman and Patterson, 1909, 1910, 1911; Patterson, 1912, 1913; Newman, 1917a, 

 1923. 



