ues produces progeny of a
deep brown, far darker than either parent. The blue may carry a factor
which brings about intensification of the brown pigment. There are
doubtless other factors which modify the brown when present, but we do not
yet know enough of the {178} inheritance of the various shades to justify
any statement other than that the heredity of the pigment in front of the
iris behaves as though it were due to a Mendelian factor.

Even this fact is of considerable importance, for it at once suggests that
the present systems of classification of eye-colours, to which some
anthropologists attach considerable weight, are founded on a purely
empirical and unsatisfactory basis. Intensity of colour is the criterion at
present in vogue, and it is customary to arrange the eye-colours in a scale
of increasing depth of shade, starting with pale greys and ending with the
deepest browns. On this system the lighter greens are placed among the
blues. But we now know that blues may differ from the deep browns in the
absence of only a single factor, while, on the other hand, the difference
between a blue and a green may be a difference dependent upon more than one
factor. To what extent eye-colour may be valuable as a criterion of race it
is at present impossible to say, but if it is ever to become so, it will
only be after a searching Mendelian analysis has disclosed the factors upon
which the numerous varieties depend.

A discussion of eye-colour suggests reflections of another kind. It is
difficult to believe that the markedly different states of pigmentation
which occur in the same species are not associated with deep-seated
chemical differences influencing the character and bent of the individual.
{179} May not these differences in pigmentation be coupled with and so
become in some measure a guide to mental and temperamental characteristics?
In the National Portrait Gallery in London the pictures of celebrated men
and women are largely grouped according to the vocations in which they have
succeeded. The observant will probably have noticed that there is a
tendency for a given type of eye-colour to predominate in some of the
larger groups. It is rare to find anything but a blue among the soldiers
and sailors, while among the actors, preachers, and orators the dark eye is
predominant, although for the population as a whole it is far scarcer than
the light. The facts are suggestive, and it is not impossible that future
res