BLASTOGENIC VARIATIONS. 133 



light and dark eye-colour, or in animals, light and dark 

 coat colour, then we can imagine the various light and 

 dark heritages from each of the parents, grandparents, 

 and more remote ancestors to be summated and bal- 

 anced against each other in each individual, and, which- 

 ever reach the higher figure, be it by ever so little an 

 amount, to be thereby enabled to originate exclusively 

 the character to which they correspond. The constitu- 

 tion of the germ-plasm of a light or dark-coloured ani- 

 mal cannot be inferred, therefore, unless the colour of 

 its ancestors be known, for it may contain anything 

 from just over half right up to the full number possible 

 of " light " or " dark " determinants. 



That exclusive inheritance obeys the law of heredity 

 in the same manner as blended inheritance seems to be 

 shown by the fact that the striking proof of the law re- 

 ferred to above was obtained by Galton for an almost 

 exclusively inherited character, viz., coat colour in Bas- 

 set hounds. Galton believed also that his data for 

 eye-colour in man afforded considerable support to the 

 law in question. Professor Pearson,* however, seems 

 to regard exclusive inheritance as distinct from blended 

 inheritance, and to look upon it as governed by a Law of 

 Reversion, and not by the law of ancestral heredity. 

 Arguing from this law, we may suppose that 25 per 

 cent, of the offspring show the full character of either 

 parent, 2 5 per cent, of them exhibit or revert to the 

 full character of each of the four grandparents, -f f per 

 cent, revert to the full character of each of the eight 

 great-grandparents, and so on. However, the whole 



*Proc. Roy. Soc., Ixvi. p. 140; also " Grammar of Science," pp. 

 486-496; also Phil. Trans. Roy. Soc. 1901, A. p. 79. 



