If you see Professor Parsons, will you thank him for the extremely liberal and fair spirit in which his Essay ('Silliman's Journal,' July, 1860.) is written. Please tell him that I reflected much on the chance of favourable monstrosities (i.e. great and sudden variation) arising. I have, of course, no objection to this, indeed it would be a great aid, but I do not allude to the subject, for, after much labour, I could find nothing which satisfied me of the probability of such occurrences. There seems to me in almost every case too much, too complex, and too beautiful adaptation, in every structure, to believe in its sudden production. I have alluded under the head of beautifully hooked seeds to such possibility. Monsters are apt to be sterile, or NOT to transmit monstrous peculiarities. Look at the fineness of gradation in the shells of successive SUB-STAGES of the same great formation; I could give many other considerations which made me doubt such view. It holds, to a certain extent, with domestic productions no doubt, where man preserves some abrupt change in structure. It amused me to see Sir R. Murchison quoted as a judge of affinities of animals, and it gave me a cold shudder to hear of any one speculating about a true crustacean giving birth to a true fish! (Parson's, loc. cit. page 5, speaking of Pterichthys and Cephalaspis, says:--"Now is it too much to infer from these facts that either of these animals, if a crustacean, was so nearly a fish that some of its ova may have become fish; or, if itself a fish, was so nearly a crustacean that it may have been born from the ovum of a crustacean?") Yours most truly, C. DARWIN. CHARLES DARWIN TO C. LYELL. Down, September 1st [1860]. My dear Lyell, I have been much interested by your letter of the 28th, received this morning. It has DELIGHTED me, because it demonstrates that you have thought a good deal lately on Natural Selection. Few things have surprised me more than the entire paucity of objections and difficulties new to me in the published reviews. Your remarks are of a different stamp and new to me. I will run through them, and make a few pleadings such as occur to me. I put in the possibility of the Galapagos having been CONTINUOUSLY joined to America, out of mere subservience to the many who believe in Forbes's doctrine, and did not see the danger of admission, about small mammals surviving there in such case. The case of the Galapagos, from certain facts on littoral sea-shells (viz. Pacific Ocean and South American littoral species), in fact convinced me more than in any other case of other islands, that the Galapagos had never been continuously united with the mainland; it was mere base subservience, and terror of Hooker and Co.