Sir John Lubbock, indeed, even suggests—­and how the suggestion would have charmed ‘Civilisation’ Buckle!—­that to this difference of food and habit the distinctive colours of the various species may very probably be due.  The ground which he adduces for this ingenious idea is a capital example of the excellent use to which out-of-the-way evidence may be cleverly put by a competent evolutionary thinker.  ‘The Baltic amber,’ he says, ’contains among the remains of many other insects a species of ant intermediate between our small brown garden-ants and the little yellow meadow-ants.  This is possibly the stock from which these and other allied species are descended.  One is tempted to suggest that the brown species which live so much in the open air, and climb up trees and bushes, have retained and even deepened their dark colour; while others, such as the yellow meadow-ant, which lives almost entirely below ground, have become much paler.’  He might have added, as confirmatory evidence, the fact that the perfect winged males and females of the yellow species, which fly about freely during the brief honeymoon in the open air, are even darker in hue than the brown garden-ant.  But how the light colour of the neuter workers gets transmitted through these dusky parents from one generation to another is part of that most insoluble crux of all evolutionary reasoning—­the transmission of special qualities to neuters by parents who have never possessed them.

This last-mentioned yellow meadow-ant has carried the system of domestication further in all probability than any other species among its congeners.  Not only do the yellow ants collect the root-feeding aphides in their own nests, and tend them as carefully as their own young, but they also gather and guard the eggs of the aphides, which, till they come to maturity, are of course quite useless.  Sir John Lubbock found that his yellow ants carried the winter eggs of a species of aphis into their nest, and there took great care of them.  In the spring, the eggs hatched out; and the ants actually carried the young aphides out of the nest again, and placed them on the leaves of a daisy growing in the immediate neighbourhood.  They then built up a wall of earth over and round them.  The aphides went on in their usual lazy fashion throughout the summer, and in October they laid another lot of eggs, precisely like those of the preceding autumn.  This case, as the practised observer himself remarks, is an instance of prudence unexampled, perhaps, in the animal kingdom, outside man.  ’The eggs are laid early in October on the food-plant of the insect.  They are of no direct use to the ants; yet they are not left where they are laid, exposed to the severity of the weather and to innumerable dangers, but brought into their nests by the ants, and tended by them with the utmost care through the long winter months until the following March, when the young ones are brought out again and placed on the young shoots of the daisy.’  Mr. White of Stonehouse has also noted an exactly similar instance of formican providence.