gratuitous. We have no inkling of the nature of such a correspondence, how it can be constituted, or in what it may consist.

Is it not time to abandon these fanciful expectations which are never realised? Everywhere both among animals and plants does the problem of specific difference reiterate itself in the same form. In view of such facts as I have related and might indefinitely multiply, the fixity of specific characters cannot readily be held to be a measure of their economic importance to their possessors. The incidence of specific fixity is arbitrary and capricious, sometimes lighting on a feature or a property which can be supposed to matter much, but as often is it attached to the most trifling of superficial peculiarities.

The incidence of variability is no less paradoxical, and without investigation of the particular case no one can say what will be found to show much or little variability. The very characteristic which in one species may exhibit extreme variability may in an allied species show extreme constancy. Illustrations will occur to any naturalist, but nowhere is this truth more strikingly presented than in the British Noctuid Moths. Many are so variable that, in the common phrase, "scarcely two can be found alike," while others show comparatively slight variation. It need scarcely be remarked that, in the instances I have in mind, the evidence of great variability is in no way due to the abundance with which the particular species occurs, for common species may show constancy, and less abundant species may show great variability. The polymorphism seems to be now at least a general property of the variable species, as the fixity is a property of the fixed species. In illustration I may refer to the following examples.