128 THE BIOLOGY OF TWINS 



at first appear, for the armor characters, which are the 

 most available features for study, are the same in both 

 sexes. There being no sex-dimorphism on the basis 

 of these characters, the inheritance from mothers is 

 equally strong for male and for female offspring. Con- 

 sequently we have every reason to believe that what 

 we discover about the inheritance from the maternal 

 side would prove to be the same as that from the paternal 

 side if the latter were known. 



Inheritance of the numbers of scutes^ — The first study 

 of inheritance of scute numbers was based upon a 

 comparison of the total number of scutes in the nine 

 bands in mother and in quadruplet offspring. A few 

 type cases may first be cited: 



Type I. Maternal number dominant: Set C 4. Mother has 

 S74 scutes; fetus I, 574; fetus II, 579; fetus III, 571; fetus IV, 

 576. — Obviously all four fetuses are extremely close to the mother 

 in this character. The resemblance is exact in the great majority 

 of individual bands. 



Type II. Paternal number dominant in all four fetuses: Set 

 K 73. Mother, 541; fetus I, 521; fetus II, 518; fetus III, 

 523; fetus IV, 520. — Obviously none of the fetuses have in- 

 herited scute numbers from the mother. Presumably they have 

 inherited it from the father, which had probably about 520 

 scutes. 



Type III. Maternal number present in some of the fetuses 

 but not in others. Three subtypes may be cited: 



I. Set K 54. Mother, 565; fetus I, 565; fetus II, 576; 

 fetus III, 569; fetus IV, 568. — This set shows three like the 

 mother and one, presumably, more like the father. 



' A study of the variability in numbers of scutes in the banded region 

 for a large sample of the species shows that a range of from 517 to 625 

 scutes and an average deviation from the mean of 15 scutes. Compare 

 with the low variability within the monozygotic sets. 



