[114] “Méchanisme du vol chez les insectes. Comment se fait la propulsion,” by Professor E. J. Marey. Revue des Cours Scientifiques de la France et de l’Etranger, for 20th March 1869, p. 254. The under surface of the wing, as will be seen from this account, not only always _looks forwards_, but it forms a true kite with the horizon, the angles made by the kite varying at every part of the down stroke, as shown more particularly at _d_, _e_, _f_, _g_; _j_, _k_, _l_, _m_ of fig. 88, p. 166. I am therefore opposed to Borelli, Macgillivray, Owen, Bishop, M. Liais, the Duke of Argyll, and Marey as to the direction and nature of the down stroke. I differ also as to the direction and nature of the up stroke. Professor Marey states that not only does the posterior margin of the wing yield _in an upward direction_ during the _down stroke_ until the under surface of the pinion makes a backward angle of 45° with the horizon, but that during the _up stroke_ it yields to the same extent _in an opposite direction_. The posterior flexible margin of the wing, according to Marey, passes through a space of 90° every time the wing reverses its course, this space being dedicated to the mere adjusting of the planes of the wing for the purposes of flight. The planes, moreover, he asserts, are adjusted not by vital and vito-mechanical acts but by _the action of the air alone_; this operating on the under surface of the wing and forcing its posterior margin _upwards_ during _the down stroke_; the air during the _up stroke_ acting upon the posterior margin of the upper surface of the wing, and forcing it _downwards_. This is a mere repetition of Borelli’s view. Marey delegates to the air the difficult and delicate task of arranging the details of flight. The time, power, and space occupied in reversing the wing alone, according to this theory, are such as to render flight impossible. That the wing does not act as stated by Borelli, Marey, and others may be readily proved by experiment. It may also be demonstrated mathematically, as a reference to figs. 114 and 115, p. 228, will show.