Since Mr. Bates first brought forward the theory of mimetic resemblances its importance has been more and more demonstrated, as it has been found how very largely animal life has been influenced in form and colour by the natural selection of the varieties that were preserved from their enemies, or enabled to approach their prey, through the resemblance they bore to something else. So general are these deceptive resemblances throughout nature, that it is often difficult to determine whether sexual preferences or the preservation of mimetic forms has been most potent in moulding the form and coloration of species, and in some the two forces are seen to be opposed in their operation. Thus in some butterflies that mimic the Heliconidae, the females only are mimetic, the males retaining the normal form and coloration of the group to which they belong. In such cases it appears as if the females have not been checked in gradually assuming the disguise they wear, and it is important that they should be protected, as they are more exposed to destruction while seeking for places to deposit their eggs; but that both sexes should not have inherited the change in form and colour when it would have been beneficial to both can only be explained, I think, on the supposition that the females had a choice of mates and preferred those that retained the primordial appearance of the group. This view is supported by the fact that many of the males of the mimetic Leptalides have the upper half of the lower wing of a pure white, whilst all the rest of the wings is barred and spotted with black, red, and yellow, like the species they mimic. The females have not this white patch, and the males usually conceal it by covering it with the upper wing, so that I cannot imagine its being of any other use to them excepting as an attraction in courtship, to exhibit to the females, and thus gratify a deep-seated preference for the normal colour of the order to which the Leptalides belong. I finally left the mines September 6th, 1872, on my way to England. I was accompanied through the forest by several of the mining officials. Though glad to return to Europe, it was not without some feeling of regret that I rode for the last time through the forest where I had so often wandered during the years I had been at Santo Domingo. The woods had become as familiar to me as home scenes. No more should I see the white-headed ruby humming-bird come darting down the brook, chasing away the green-throat from its bathing-place; no more watch the flocks of many-coloured birds hunting the insects in the forests, or admire the wonderful instincts of the tropical ants. I listened with pleasure to the last hoarse cries of the mot-mots, and tried to impress on my memory the curious forms of vegetation--the palms, the gigantic arums, the tangled lianas, and perching epiphytes.