I have given your opinion on continuous land, I see, too strongly.
LETTER 50. TO S.P. WOODWARD. Down, July 18th [1856].
Very many thanks for your kindness in writing to me at such length, and I am glad to say for your sake that I do not see that I shall have to beg any further favours. What a range and what a variability in the Cyrena! (50/1. A genus of Lamellibranchs ranging from the Lias to the present day.) Your list of the ranges of the land and fresh-water shells certainly is most striking and curious, and especially as the antiquity of four of them is so clearly shown.
I have got Harvey's seaside book, and liked it; I was not particularly struck with it, but I will re-read the first and last chapters.
I am growing as bad as the worst about species, and hardly have a vestige of belief in the permanence of species left in me; and this confession will make you think very lightly of me, but I cannot help it. Such has become my honest conviction, though the difficulties and arguments against such heresy are certainly most weighty.
LETTER 51. TO C. LYELL. November 10th [1856].
I know you like all cases of negative geological evidence being upset. I fancied that I was a most unwilling believer in negative evidence; but yet such negative evidence did seem to me so strong that in my "Fossil Lepadidae" I have stated, giving reasons, that I did not believe there could have existed any sessile cirripedes during the Secondary ages. Now, the other day Bosquet of Maestricht sends me a perfect drawing of a perfect Chthamalus (a recent genus) from the Chalk! (51/1. Chthamalus, a genus of Cirripedia. ("A Monograph on the Sub-class Cirripedia," by Charles Darwin, page 447. London, 1854.) A fossil species of this genus of Upper Cretaceous age was named by Bosquet Chthamalus Darwini. See "Origin," Edition VI., page 284; also Zittel, "Traite de Paleontologie," Traduit par Dr. C. Barrois, Volume II., page 540, figure 748. Paris, 1887.) Indeed, it is stretching a point to make it specifically distinct from our living British species. It is a genus not hitherto found in any Tertiary bed.
LETTER 52. TO T.H. HUXLEY. Down, July 9th, 1857.
I am extremely much obliged to you for having so fully entered on my point. I knew I was on unsafe ground, but it proves far unsafer than I had thought. I had thought that Brulle (52/1. This no doubt refers to A. Brulle's paper in the "Comptes rendus" 1844, of which a translation is given in the "Annals and Mag. of Natural History," 1844, page 484. In speaking of the development of the Articulata, the author says "that the appendages are manifested at an earlier period of the existence of an Articulate animal the more complex its degree of organisation, and vice versa that they make their appearance the later, the fewer the number of transformations which it has to undergo.") had a wider basis for his generalisation, for I made the extract several years ago, and I presume (I state it as some excuse for myself) that I doubted it, for, differently from my general habit, I have not extracted his grounds. It was meeting with Barneoud's paper which made me think there might be truth in the doctrine. (52/2. Apparently Barneoud "On the Organogeny of Irregular Corollas," from the "Comptes rendus," 1847, as given in "Annals and Mag. of Natural History," 1847, page 440. The paper chiefly deals with the fact that in their earliest condition irregular flowers are regular. The view attributed to Barneoud does not seem so definitely given in this paper as in a previous one ("Ann. Sc. Nat." Bot., Tom. VI., page 268.) Your instance of heart and brain of fish seems to me very good. It was a very stupid blunder on my part not thinking of the posterior part of the time of development. I shall, of course, not allude to this subject, which I rather grieve about, as I wished it to be true; but, alas! a scientific man ought to have no wishes, no affections--a mere heart of stone.
There is only one point in your letter which at present I cannot quite follow you in: supposing that Barneoud's (I do not say Brulle's) remarks were true and universal--i.e., that the petals which have to undergo the greatest amount of development and modification begin to change the soonest from the simple and common embryonic form of the petal--if this were a true law, then I cannot but think that it would throw light on Milne Edwards' proposition that the wider apart the classes of animals are, the sooner do they diverge from the common embryonic plan--which common embryonic [plan] may be compared with the similar petals in the early bud, the several petals in one flower being compared to the distinct but similar embryos of the different classes.