260 



MOTIONS OF INSECTS. 



before rain named the Gecko 1 (Lacerta Gecko), could walk 

 against gravity up the walls of houses ; and comparing this 

 with the parallel motions of flies, he was desirous of having 

 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, sufficient to cause atmo- 

 spheric 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 con- 

 traction ; they are concavo-convex, with serrated edges, the 

 concave 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 ap- 

 plying this closely to the plane of position, the air is suffi- 

 ciently 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 



1 Amain. Acad. i. 549. The Gecko, probably, is not the only lizard that walks 

 against gravity. St. Pierre mentions one not longer 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. These lizards are some- 

 times so tame that they will feed out of the hand. (Voyage, &c. 73.) Major 

 Moor and Captain Green observed similar lizards in India, that ran 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 endeavoured 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 examined this animal in Egypt, assures me that this ac- 

 count of Hasselquist's, as far as it relates to the venom of the Gecko, is not cor- 

 rect. 



