443 



occur likewise. There are however also families (table V) for whom 

 this is not the case, likewise families are met with (table VI), for 

 whom the indices differ very little, bat are somewhat higher than 

 those that hold for dolichocephaly. Consequently we cannot admit 

 beside segregation simple dominance of brachycephaly. 



The cases mentioned already (table Vll), where the indices of 

 children surpass those of the parents, either on one or on both sides 

 are especially in favour of the possibility, that the inheri fancy is 

 determined by a series of factors working in the same sense, which 

 each individually give an intermediary first bastard-generation (F.^). 

 This method of explanation can moreover very well be applied 

 to other phenomena of our material. The great variability of the 

 indices of the children and the slight differences of those of the 

 parents (table I) can e.g. be occasioned by the fact that the parents 

 contain the factors in a heterozygotic form, so that exteriorly they 

 are intermediary. Consequently different homozygotic, thus greatly 

 divergent values of indices, will occur among the children. The 

 separate occurrence of a strongly deviating index-value is caused, 

 according to this view, by the rare combination of two or more 

 factors working in the same direction in a homozygotic form (one 

 of the 16 cases in the dihybridic scheme, one of the 64 cases in 

 the trihybridic one). The slight mutual differences of the tables 111 

 and VI can be explained by admitting, that the forms of issue contain 

 nearly the same factors, so that consequently no new divergent 

 combinations occur in the children. The cases of table VIII contain- 

 ing examples of extreme values of indices of one of the parents 

 may be explained in the same way. A very low index-value is 

 caused by the deficiency of, a very high one by the existence in 

 homozygotic form of some factors working in the same direction. 

 It is consequently clear that among the children, as a rule, the 

 extreme value will not occur. 



What gives likewise significance to this manner of explanation, 

 is the possibility of explaining the limitedness of the selection : by 

 selection no more can be reached than the form that contains all 

 the factors of heredity working in the same direction in a homo- 

 zygotic form. Examples in our material of "selection-working" (ac- 

 cording to Niisson-Ehle's explanation, consequently of combination 

 of factors) are the fam. Ill and XXXIV (vide the genealogical trees, 

 p. 448). The parents and eleven children of fam. XXXIV have 

 rather low indices viz. the parents 79 and the children 72 — 79. 

 If now we admit that the parents possess each a different factor 

 for brachycephaly, with which consequently absence of a similar 



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