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of white speckles on elbow joint — in Bewick drawing¹ the the rock Pidgeon has not: now how many wild pidgeon have spangles on this part: this will be well worth working out. —

Study Temmincks² work on Pidgeons, & see whether feathered legs, — carruncles on beak as in Muscovy duck, crested feather, pouters, fan tails, are found in any colours of plumage &c &c. Pouting pidgeon exaggeration of cooing. — & compare them with all the varieties. — Habits of rock pidgeon. — (I suspect Pennant³ has described them) — (Study horns of wild cattle. — & plumage of fowls — long ears of rabbits. — & long fur. — feathers on legs of Ptarmigan & in Bantam. — ) In the Pidgeons trace the washing out of the forked band, like in plumage of ducks. —

¹ Ann. Mag. Nat. Hist., vol. 2, 1838, p. 174.
² Coenraad Jacob Temminck, Histoire naturelle générale des pigeons.
³ Thomas Pennant, Genera of Birds, Edinburgh, 1773.

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M^r Yarrell says in very close species of birds, habits when well watched always very different. — the two redpoles can hardly be told apart, so that after differences were pointed out Selby confounded them, yet can readily be told by incubation & other peculiarities. —

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Lyells Elements.¹ p. 290 D^r Beck on numerical proportion in shells in Arctic Ocean, p. 350 Grallae in Wealden oldest birds, p. 411 Decapod Crust in Muschel-kalk & 5 genera of reptiles. — Me p. 417 Magnesian limestone & Zechstein oldest rocks in which reptiles have been found. p. 426. Sauroid fish in coal, true fish & not intermediate between fish & reptile — yet osteology closely resembles reptiles. p. 432 some plants in coal supposed to be intermediate between coniferous trees & Lycopodium. — p. 437 Many existing genera of shells in the mountain limestone (how different from plants!) But the Cephalopoda depart more widely from living forms. — p. 458 Upper Silurian fishes oldest formation highly organized. —

¹ Sir Charles Lyell, Elements of Geology, London, 1838.

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do. p. 461 Lower Silurian — several existing genera — Nautilus, Turbo, buccinum, turritella, terebratula, orbicula, with many extinct forms & Trilobites.

Sept. 25^th In considering infertility of hybrids inter se. the first cross generally brothers & sisters & therefore somewhat unfavourable. —

28^th We ought to be far from wondering of changes in numbers of species, from small changes in nature of locality. Even the energetic language of Malthus Decandolle does not convey the warring of the species as inference from Malthus. — increase of brutes must be prevented solely by positive checks, excepting that famine may stop desire. — in nature production does not increase, whilst no check prevail, but the positive check of famine & consequently death.

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Population is increase at geometrical ratio in far shorter time than 25 years — yet until the one sentence¹ of Malthus no one clearly perceived the great check amongst men. — there is spring, like food used for other purposes as wheat for making brandy. — Even a few years plenty, makes population in Men increase & an ordinary crop causes a dearth. take Europe on an average every species must have same number killed year with year by hawks, by cold &c. — even one species of hawk decreasing in number must affect instantaneously all the rest. — The final cause of all this wedging, must be to sort out proper structure, & adapt it to changes. — to do that for form, which Malthus shows is the final effect (by means however of volition) of this populousness on the energy of man. One may say there is a force like a hundred thousand wedges trying force into every kind of adapted structure into the gaps of in the oeconomy of nature, or rather forming gaps by thrusting out weaker ones. —

¹ This note, written on 28 September 1838, makes it possible to identify the sentence in T. R. Malthus's Essay on the Principle of Population which enabled Darwin to see how the pressure of natural selection is inevitably brought to bear. It was in the 6th edition, London 1826 1: 6: "It may safely be pronounced, therefore, that the population, when unchecked, goes on doubling itself every twenty five years, or increases in a geometrical ratio."

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D'Orbigny¹ Comtes Rendus p. 569. 1838 says the cross between the Guaranis & Spaniards are almost white from first generation, that with Quichuas the American character is more tenacious & does not disappear for many generations.

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Sept 29^th Dr Andrew Smith. Remarks on extraordinary curiosity of Monkeys. The Baboon of which anecdotes have been told is Cynocephalus Porcarius. — This monkey did not like a great coat made for it at first, but in two or three days learn its comfort & though could not put it on, yet threw it over

¹ Alcide Dessalines D'Orbigny, "L'Homme américain (de l'Amérique méridionale),eonsidéré sous ses rapports physiologiques et moraux ", Comptes Rendus Acad. Sci. Paris tome 7, 1838, p. 569.