142 NATURAL INHERITANCE. [CHAP. 



curves that exactly represented the true Eye-colours for 

 the four generations, they would either be concurrent 

 or they would not. If these curves were concurrent, 

 the errors in the R.F.F. data must have been so 

 curiously distributed as to preserve the concurrence. 

 If these curves were not concurrent, then the errors 

 in the R.F.F. data must have been so curiously distri- 

 buted as to neutralise the non-concurrence. Both of 

 these suppositions are improbable, and we must con- 

 clude that the curves really agree, and that the R.F.F. 

 errors are not large enough to spoil the agreement. 

 The close similarity of the two curves, derived respec- 

 tively from the whole of the male and the whole of 

 the female data, and the more perfect form of the curve 

 derived from the aggregate of all the cases, are 

 additional evidences in favour of the goodness of the 

 data on the whole. 



Fundamental Eye-colours. It is agreed among writers 

 (cf. A. de Candolle, see footnote overleaf) that the one 

 important division of eye-colours is into the light and 

 the dark. The medium tints are not numerous, but 

 may be derived from any one of four distinct origins. 

 They may be hereditary with no notable variation, they 

 may be varieties of light parentage, they may be 

 varieties of dark parentage, or they may be blends. 

 Medium tints are classed in my list under the heading 

 "4. Dark grey, hazel;" these form only 12 '7 per 

 cent, of all the observed cases. In medium tints, the 

 outer portion of the iris is often of a dark grey colour, 



