MOTIONS OF INSECTS. 457 
But, he proceeds, in the decline of the year this resistance becomes too 
mighty for their diminished strength ; and we see tlies labouring along, 
and lugging their feet in windows as if they stuck fast to the glass. 
Sir Joseph Banks, to whom every branch of Natural History has been 
so much indebted, excited an inquiry, the results of which confirmed 
Derham’s system concerning this motion of animals against gravity. When 
abroad, he had noticed that a lizard, on account of the sound that it emits 
before rain, named the Gecko? (Lacerta Gecko), could walk against gravity up 
the walls of houses ; and comparing this with the parallel motions of flies, he 
was desirous of haying the subject more scientifically illustrated than it 
had been. This inquiry was put into the hands of Sir Everard Home, 
who was assisted in it by the incomparable pencil of Mr. Bauer; and it 
was proved most satisfactorily that it is by producing a vacuum between 
certain organs destined for that purpose and the plane of position, suffi- 
.cient to cause atmospheric pressure upon their exterior surface, that the 
animals in question are enabled to walk up a polished perpendicular, like 
the glass in our windows, and the chunam walls in India, or with their 
backs downward on a ceiling, without being brought to the ground by the 
weight of their bodies. 
The instruments by which a fly effects this purpose are two suckers. 
connected with the last joint of the tarsus by a narrow infundibular neck, 
which has power of motion in all directions, immediately under the root of 
each claw. These suckers consist of a membrane capable of extension. 
and contraction ; they are concavo-convex, with serrated edges, the con- 
cave surface being downy, and the convex granulated. When in action 
they are separated from each other, and the membrane expanded so as to- 
increase the surface ; by applying this closely to the plane of position, the 
air is sufficiently expelled to produce the pressure necessary to keep the 
animal from falling. When the suckers are disengaged, they are brought. 
together again so as to be confined within the space between the two claws. 
This may be seen by looking at the movements of a fly in the inside of a glass 
tumbler with a common microscope.’ Thus the fly, you see, does no more 
than the leech has been long known to do, when moving in a glass vessel. 
Furnished with a sucker at each extremity, by means of these organs it 
marches up and down at its pleasure, or as the state of the atmosphere 
inclines it. 
1 Nat. Hist. ii, 274. 
2 Amen. Acad, i. 549. The Gecko, probably, is not the only lizard that walks 
against gravity. St. Pierre mentions one not loiter than a finger, that, in the Isle 
of France, climbs along the walls, and even up the glass, after the flies and other 
insects, for which it watches with great patience. hese lizards are sometimes so 
tame that they will feed out of the hand. (Voyage, &c. 73.) Major Moor and 
Captain Green observed several lizards in India, that run up the walls and over the 
ceilings after the mosquitos. Hasselquist says that the Gecko is very frequent at 
Cairo, both in the houses and without them, and that it exhales a very deleterious 
poison from the lobuli between the toes. He saw two women and a girl at the 
point of death, merely from eating a cheese on which it had dropped its venom. 
One ran over the hand of a man, who endeayoured to catch it; and immediately 
little pustules, resembling those occasioned by the stinging-nettle, rose all over the 
parts the creature had touched. (Voyage, 220,) M. Savigny, however, who exa~ 
mined this animal in Egypt, assures me that this account of Hasselquist’s, as far as 
it relates to the venom of the Gecko, is not correct. 
5 Philos. Trans. 1816, 825. t. xviii. f. 1—7. 
@ Mr. Blackwall, ina paper “ On the Pulvilli of Insects,” having found that flies 
