The observations and experiments recorded in the present volume date from 1864. In 1867 I lectured on the subject of animal mechanics at the Royal Institution of Great Britain:[7] in June of the same year (1867) I read a memoir “On the Mechanism of Flight” to the Linnean Society of London;[8] and in August of 1870 I communicated a memoir “On the Physiology of Wings” to the Royal Society of Edinburgh.[9] These memoirs extend to 200 pages quarto, and are illustrated by 190 original drawings. The conclusions at which I arrived, after a careful study of the movements of walking, swimming, and flying, are briefly set forth in a letter addressed to the French Academy of Sciences in March 1870. This the Academy did me the honour of publishing in April of that year (1870) in the Comptes Rendus, p. 875. In it I claim to have been the first to describe and illustrate the following points, viz.:-- [7] “On the various modes of Flight in relation to Aëronautics.”--Proceedings of the Royal Institution of Great Britain, March 22, 1867. [8] “On the Mechanical Appliances by which Flight is attained in the Animal Kingdom.”--Transactions of the Linnean Society, vol. xxvi. [9] “On the Physiology of Wings.”--Transactions of the Royal Society of Edinburgh, vol. xxvi. That quadrupeds walk, and fishes swim, and insects, bats, and birds fly by figure-of-8 movements. That the flipper of the sea bear, the swimming wing of the penguin, and the wing of the insect, bat, and bird, are screws _structurally_, and resemble the blade of an ordinary screw-propeller. That those organs are screws _functionally_, from their twisting and untwisting, and from their rotating in the direction of their length, when they are made to oscillate. That they have a reciprocating action, and reverse their planes more or less completely at every stroke. That the wing describes _a figure-of-8 track_ in space when the flying animal is artificially fixed. That the wing, when the flying animal is progressing at a high speed in a horizontal direction, describes _a looped_ and then _a waved track_, from the fact that the figure of 8 is gradually opened out or unravelled as the animal advances. That the wing acts after the manner of a kite, both during the down and up strokes.