In my last letter I think I mentioned to you that I had worked out and sent home to the President of the Linnean Society, through Captain Stanley, an account of Physalia, or Portuguese man-of-war as it is called, an animal whose structure and affinities had never been worked out. The careful investigation I made gave rise to several new ideas covering the whole class of animals to which this creature belongs, and these ideas I have had the good fortune to have had many opportunities of working out in the course of our subsequent wanderings, so that I am provided with materials for a second paper far more considerable in extent, and embracing an altogether wider field. This second paper is now partly in esse--that is, written out--and partly in posse--that is, in my head; but I shall send it before leaving. Its title will be "Observations upon the Anatomy of the Diphydae, and upon the Unity of Organisation of the Diphydae and Physophoridae," and it will have lots of figures to illustrate it. Now when we return from the north I hope to have collected materials for a much bigger paper than either of these, and to which they will serve as steps. If my present anticipations turn out correct, this paper will achieve one of the great ends of Zoology and Anatomy, namely, the reduction of two or three apparently widely separated and incongruous groups into modifications of the single type, every step of the reasoning being based upon anatomical facts. There! Think yourself lucky you have only got that to read instead of the slight abstract of all three papers with which I had some intention of favouring you. [These papers are to be found in volume 1 of the "Scientific Memoirs" of T.H. Huxley page 9.] But five years ago you threw a slipper after me for luck on my first examination, and I must have you to do it for everything else. [At the Cape a stay of a month was made, from March 6 to April 10, and certain surveying work was done, after which the "Rattlesnake" sailed for Mauritius. In spite of the fact that the novelty of tropical scenery had worn off, the place made a deep impression. He writes to his mother, May 15, 1847:--]