1875.) Aérial Locomotion. EY 
Marey, is the reply, claims to have been the first to describe 
and illustrate the following :— 
“yr, That quadrupeds walk, and fishes swim, and insects, bats, and birds 
fly, by figure-of-8 movements.” 
“2, 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.” 
“3. That these organs are screws functionally, from their twisting and un- 
twisting, and from their rotating in the direction of their length, when 
they are made to oscillate.” 
“4, That they have a reciprocating action, and reverse their planes more or 
less completely at every stroke.” 
“5. That the wing describes a figure-of-8 track in space, when the flying 
animal is artificially fixed.” 
«© 6. 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 fac that the figure of 8 is gradually opened out or unra- 
velled as the animal advances.” 
“7. That the wing acts after the manner of a boy’s kite,” both ‘ during the 
down’ and the ‘up’ strokes.* 
Such are briefly Dr. Pettigrew’s views; and if we com- 
pare what Professor Marey has written on flight with what 
Dr. Pettigrew here enunciates, we shall find the coincidences 
{to use no stronger terms) very striking. 
Take the following passages from Professor Marey’s 
recent work as examples :— 
“Tf we gild a large portion of the upper surface of a wasp’s wing, taking 
precautions that the gold leaf should be limited to this surface only, we see that 
the animal placed in the sun’s rays gives the figure-of-8 with a very unequal 
intensity in the two halves of the image..... It is evident that the cause 
of the phenomenon is to be found in a change in the plane of the wing, and 
consequently in the incidence of the solar rays..... We shall find in the 
employment of the graphic method new proofs of changes in the plane of the 
wing during flight..... [In this and other quotations the italics are ours. ] 
It is therefore not necessary to look for special muscular actions to produce 
changes in the plane of the wing ; these in their turn will give us the key to the 
oblique curvilinear movements which produce the figure-of-8 course followed by 
the inseét’s wing.” —(‘‘ Animal Mechanism,” pp. 188, 197). 
In the passages here cited, Professor Marey admits, not 
only that the wing of the insect makes a figure-of-8 track in 
space, but also that the figure-of-8 is produced by a change of 
plane in the wing. 
This is an important admission, for Professor Marey 
copies at page 201 of his book a figure-of-8 representation 
from Dr. Pettigrew’s 1867 memoir,t in which this change of 
plane is delineated, and states that the arrows in Dr. 
Pettigrew’s figure all point in one dire<tion, and are wrongly 
* “On the Physiology of Wings.” By J. BELL Petticrew, M.D., F.R.S. 
Trans. Roy. Soc. of Edinburgh, vol. xxvi., p. 332. 
t Marey’s figure is “ Fig. 86, Trajectory of the Wing,” p. 201. Pettigrew’s 
figure is at p. 233. Trans. Linn. Soc., 1867., vol. xxvi. 
