Dear Sir,—During the very delightful excursion in your “Medusa,” in which I had, with two of our friends, the pleasure of accompanying you through some of the western lochs of Scotland, we had not only many opportunities of admiring the special beauties of your country, but also many periods devoted to scientific work and to scientific discussions. You were good enough to demonstrate to us your ingenious methods of determining deep-sea temperatures. You dredged in our presence masses of beautiful shining Schizopods, and also before our eyes you formed the once so famous Bathybius Huxleyi. We conversed on general principles of natural philosophy, and on the different modes of regarding organic life and organic forms. You then invited me to give you a written explanation of my own morphological views—an invitation which I propose to aocept in the following pages.