I then began my book, but considering myself still a painter by profession, I gave comparatively little time to writing, and got on but slowly. I left England for North Italy in the middle of May 1876 and returned early in August. It was perhaps thus that I failed to hear of the account of Professor Hering’s lecture given by Professor Ray Lankester in _Nature_, July 13 1876; though, never at that time seeing _Nature_, I should probably have missed it under any circumstances. On my return I continued slowly writing. By August 1877 I considered that I had to all intents and purposes completed my book. My first proof bears date October 13, 1877. At this time I had not been able to find that anything like what I was advancing had been said already. I asked many friends, but not one of them knew of anything more than I did; to them, as to me, it seemed an idea so new as to be almost preposterous; but knowing how things turn up after one has written, of the existence of which one had not known before, I was particularly careful to guard against being supposed to claim originality. I neither claimed it nor wished for it; for if a theory has any truth in it, it is almost sure to occur to several people much about the same time, and a reasonable person will look upon his work with great suspicion unless he can confirm it with the support of others who have gone before him. Still I knew of nothing in the least resembling it, and was so afraid of what I was doing, that though I could see no flaw in the argument, nor any loophole for escape from the conclusion it led to, yet I did not dare to put it forward with the seriousness and sobriety with which I should have treated the subject if I had not been in continual fear of a mine being sprung upon me from some unexpected quarter. I am exceedingly glad now that I knew nothing of Professor Hering’s lecture, for it is much better that two people should think a thing out as far as they can independently before they become aware of each other’s works but if I had seen it, I should either, as is most likely, not have written at all, or I should have pitched my book in another key.