240 Aérial Locomotion. (April, 
but unless the wings themselves fly forward in curves, both 
during the down and up strokes, as Dr. Pettigrew explains, 
the body cannot be transmitted from one point to another. 
Dr. Pettigrew’s experiments with natural and artificial 
wings are quite decisive on this point, as we have ourselves 
verified. 
Dr. Pettigrew was likewise the first to describe and figure 
the ellipse formed by the wing of the bird, and to point out 
the difference in the direétion of the stroke in the wing of 
the bird and inse¢t, the stroke in the insect being, as a rule, 
nearly horizontal, that in the bird nearly vertical.* 
Professor Marey, in his first paper on flight, communi- 
cated to the French Academy of Sciences,+ delineates the 
wings of the wasp as making vertical figure-of-8 loops. 
Now this never happens in the wasp. The figure-of-8 loops 
made by the wing of the wasp, as Dr. Pettigrew has shown, 
are so oblique as to be nearly horizontal. 
Professor Marey, in his latest work, has corrected this 
mistake{, and has delineated the horizontal figure-of-8 loops 
made by the wing of the insect in a figure nearly, if not. 
identical, with a similar figure by Dr. Pettigrew. 
Professor Marey’s figure occurs at page 200 of his new 
work (1874), that of Dr. Pettigrew’s at page 338 of his 
memoir, ‘‘ On the Physiology of Wings.” (Trans. Roy. Soc. 
Bding vol xxvil..1670) | 
A careful comparison of the figures in question will show 
that Professor Marey’s figure is, or may be, a transcript of 
Dr. Pettigrew’s. And this remark applies not only to the 
figure as a whole, but to all its details; first, to the hori- 
zontal direction of the figure-of-8 loops, made by the wing 
* The following is the account given by Dr. Pettigrew: ‘‘ The direction of 
the stroke varies slightly according to circumstances, but it will be quite 
proper to assume that the wing of the insect is made to vibrate in a more or 
less horizontal direGtion, and that of the bird or bat in a more or less vertical 
direction. By a slight alteration in the position of the body, or by a rotation 
of the wing in the direétion of its length, the vertical direction of the stroke is 
converted into a horizontal direction, and vice versa. 
“The facility with which the direction of the stroke is changed is greatest in 
inse&ts; it is not uncommon to see them elevate themselves by a figure-of-8 
horizontal screwing motion, and then suddenly changing the horizontal 
screwing into a more vertical one, to dart rapidly forward in a curved line.”— 
Trans. Roy. Soc. Edin., vol. xxvi., p. 335. 
+ Physiologie—Détermination éxperimentale du movement des ailes des 
inseétes pendant le vol. Par M. E. J. Marry. Comptes Rendus, tom. Ixvii., 
No. 26, December 28th, 1868, p. 1341. 
+ Professor Marey remarks—* We need only observe the flight of certain 
insects, the common fly for instance, and most of the other Diptera, to see that 
the plane in which the wings move is mo# vertical, but, on the contrary, very 
nearly hovizontal.”—(Animal Mechanism, 1874, p. 204). 
|| Figs. 5 and 6 more especially. 
