196 H. H. NEWMAN. 



definite in numbers and arrangement long before birth. How 

 fortunate a circumstance it is that this species, which is unique 

 in its polyembryonic method of reproduction, should at the same 

 time be unique in its possibilities for biometric treatment! I 

 was especially impressed with this fact lately when I tried to get 

 some basis for a comparison between cattle twins and could 

 find nothing satisfactory for the purpose. The same would be 

 true for sheep, cats or any other mammal. Differences in size, 

 the only measurable differences in these species, are quite unsafe 

 criteria for the determination of coefficients of correlation, since 

 they are notoriously affected by differences in nutrition. Al- 

 though any part of the integument of the armadillo is superior 

 for the establishment of correlation constants to anything found 

 in any other mammal, the banded region, on account of its 

 regularity, definiteness and specific fixity, is preeminently adapted 

 for the study of inheritance and of the degrees of resemblance and 

 difference among individuals of a polyembryonic set. 



So regular is the banding that it would be impossible to dis- 

 cover any symmetry in the bilateral arrangement of integumen- 

 tary structures were it not for the occurrence of occasional band 

 irregularities (double bands) and of fairly frequent double scutes. 

 These peculiarities of the integument furnish landmarks for the 

 study of symmetry relations that are quite uniquely suitable for 

 such studies and are more readily comparable than are the finger- 

 print patterns of human duplicate twins that have been used 

 for a similar type of study. 



(&) Irregularities in the Inheritance of Band and Scute Anom- 

 alies. That band and scute anomalies are definitely inherited is 

 proven by the fact that anomalies are always present in offspring 

 of mothers that show the anomaly. The real problem is to 

 explain why all four features of a set of quadruplets do not inherit 

 these anomalies equally and in the same form. Since they come 

 from a single fertilized egg they have the same genetic consti- 

 tution and should be identical unless there exist certain agencies 

 that result in an irregular distribution of the differentiating factor 

 responsible for anomalies. That these agencies which produce 

 irregular distribution of anomalies among the individuals of a 

 set are not environmental is certain, for there appears to be no 



