126 THE BIOLOGY OF TWINS 



sets? (c) According to what laws are such characters 

 inherited ? In the briefest possible way an attempt 

 will be made to present an outline of some of the studies 

 on heredity in armadillos which have been published in 

 several recent papers.' 



MATERIALS FOR THE STUDY OF HEREDITY 



No other animal is so beautifully adapted as is the 

 armadillo for the detailed and accurate comparison of 

 parent and offspring or of offspring among themselves. 

 The strikingly diagrammatic arrangement of the integu- 

 ment into five armor shields (see frontispiece), each 

 shield consisting of well-defined units (scutes or scales), 

 furnishes an unparalleled opportunity for the study of 

 inter- and intra-individual correlation. These charac- 

 ters, moreover, are definitive in number and arrange- 

 ment long before birth. How fortunate a circumstance 

 that this species, which has so unique a method of 

 reproduction, should also possess equally unique pos- 

 sibilities for biometric treatment! 



Although any part of the armor would serve well 

 the purposes in hand, the banded region, on account 

 of its regularity and clean-cut character, seems almost 

 made to order for biometric study. Each band is 

 made up of from 50 to 70 units, here called scutes. A 

 scute consists of a horny scale, a bony base, and a 

 definitely arranged group of hairs. For our purposes 

 this whole complex may be viewed as a unit character. 

 Studies have been made of the specific variability in 

 total numbers of scutes in the nine bands and of that 



^ H. H. Newman, Biological Bulletin, XXIX, Nos. i and 2; ibid.^ 

 Journal of Experimental Zoology, XV, No. 2. 



