INHERITANCE OF VARIATES IN THE ARMADILLO 147 



6. Is there a real difference in the absolute variability of the 

 two sexes? 



7. To what extent is sexual dimorphism a factor in disturbing 

 the inheritance ratios in connection with the characters dealt with 

 in this study? 



8. To what extent may resemblances and differences among 

 the individuals of a given set of quadruplets be a product of envi- 

 ronmental similarity or diversity? 



GENERAL INTRODUCTION 



In a paper entitled ' ' The limits of hereditary control in arma- 

 dillo quadruplets" (Newman and Patterson '11) the authors pre- 

 sented a statistical study of the variations of the scutes in the 

 nine bands of armor in twenty sets of armadillo quadruplets. The 

 fact that in each case the four members of a set were known to be 

 the product of the division of a single fertilized egg gave especial 

 interest to a detailed comparison of the members of the various 

 sets. It was assumed that in so far as the four individuals of a 

 given set were alike this similarity was predetermined prior to the 

 separation of the four embryonic primordia, and in so far as they 

 were different their differences were attributable to divergent epi- 

 genetic factors operating during or subsequent to the period of 

 segregation. It was possible to show that with respect to the 

 total number of scutes in the nine movable bands the coefficient 

 of correlation for quadruplets was 0.9348, a degree of correlation 

 higher than that determined for any inter-individualistic relation 

 and paralleled only by those obtaining between structures of the 

 right and left hand sides of the same individual. This coefficient 

 of correlation was taken to be an index of hereditary control, in the 

 sense that it indicates just how nearly perfect in operation is the 

 predeterminative mechanism. It was also stated that the align- 

 ment of scutes into the respective rows or bands is probably not 

 predetermined to any large extent but is probably due for the 

 most part to mechanical pressures incident to growth, factors 

 purely epigenetic in character, a statement the validity of which 

 is not borne out by the present investigation. 



