439 



If now we pass to the examination of the behaviour of heredit}' 

 of the headform of the material at our disposal, then we follow, 

 when doing so, the way taken by other investigators (Rüdin, 

 Davenport, Lündborg) : we examine if the data admit of a Mendëlian 

 explanation. We assume in this respect that the index of length- 



Fig. 6. 

 169 brothers and 169 sisters. Of each family as 

 many brothers as sisters have been inserted. 



width types the headform. A. Retzius has answered to the objection ^) 

 that the index represents only two dimensions, that experience 

 teaches the index may in reality be taken as the expression of the 

 headform. Another question is, whether the Mendelian analysis of 

 the factors of heredity of the shape of the head can restrict itself to 

 trace the heredity of the index. In this case we should have to do 

 here with one pair of units of heredity (for the large and small 

 index, or for several different large indices). If the length and the 

 width mendel separately, we have to do either with two pairs of 

 units of heredity or with two progressions of it (respectively for the 

 large and the small length and idem width or for several different 

 large lengths and different large widths). Both possibilities will be 

 examined. If the length and the width of the head mendel sepa- 

 rately phenomena of segregation will come to expression in the index. 

 We begin by tracing these. This gives us the advantage, that the 

 complete material, likewise that of not fullgrown persons, can be 

 considered. In the tlrst place we examine if there is segregation. 

 In favour of segregation plead these cases where, with little differences 

 in the indices of the parents, the children show a great divergence 

 of values, or if a single child has a strongly deviating index. In 

 the tables I and II some of these cases are collected. 



^) A. Retzius, I.e. S. 57. 



