198 HALFDAN BRYN 



type of »mixed» eyes, all the children get the same type of 

 »mixed» eyes. 



6. In our population there are probably three biological types with 

 regard to eye colour: 



a. the plain blue type, 



b. the plain brown type, 



c. the light »mixed» type, where there is a narrow, but well de- 

 fined brown ring around the pupil, while the rest of the iris 

 is blue. 



7. These different eye types interbreed in accord with the Mendelian 

 laws of heredity, viz. blue eyes are recessive to all types of eyes 

 with brownish pigment. 



II. THE GENETIC RELATION OF INDEX CEPHALICUS. 



In this paper an attempt is made to explain the genetic relation 

 of the width-length index of the head within a Norwegian population. 

 The two districts from where the material is gattered are Selbu and 

 Tydalen. Though Selbu and Tydalen are two neighbouring districts 

 in the same valley they differ very much with regard to the size of 

 this index. One district, Selbu, must be characterized as rather 

 brachycephalic, the index is at any rate relatively high or 80, i. 



The other district, Tydalen, has an index of 76,9, which must be- 

 considered relatively low when it is remembered that the average in- 

 dex of the entire country is about 78,o. 



Researches made during many years prove that the two indices 

 mentioned above are constant. 



This may seem rather strange in view of the fact that the two 

 districts are neighbouring districts of the same valley. They have been 

 inhabited very long, Selbu for about two thousand years, and Tydalen 

 for a thousand years at least. The populations of the two districts live, 

 however, rather isolated. Individuals from the two districts very 

 rarely intermarry. It should be added, that Selbu has got its popula- 

 tion from thê^districts round the fjord of Trondhjem, whereas the po- 

 pulation of Tydalen has chiefly come across the mountains from the 

 south part of Norway. 



Therefore the population of Selbu must be considered a rather 

 homogeneous mass with the index 80,i. The population of Tydalen 

 is also supposed to be a homogeneous mass, but with the index 76,9. 



