Since the season of 1894 (when I first discovered that the upper and lower membranes of a butterfly's wing could be separated), I have had a desire to test the accuracy of the conclusions reached by me at that time; so with the remarkable profusion of Anosia (Danais) Archippus, Fab., in the season of 1899, I was able to secure such an abundance of material to work with that I could repeat the observations until every doubt was satisfactority settled. I shall only give here a brief statement of results reached, as a full account of the various processes will be published in the forthcoming Annual Report of the Society for 1899.