320 MOTIONS OF INSECTS. 



Dr. Derham, seems to have been one of the first who 

 gave the true solution of this enigma. " Flies," says he, 

 " besides their sharp hooked nails, have also skinny 

 palms to their feet, to enable them to stick on glass and 

 other smooth bodies, bji the pressure of the atmosphere*" 

 He compares these palms to the curious suckers of male 

 Dytisci, before alluded to, and illustrates their action by 

 a common practice of boys, who carry stones by a wet 

 piece of leather applied to their top. Another eminent 

 and excellent naturalist, the late Mr. White, adopted 

 this solution. He observes that in the decline of the 

 year, when the mornings and evenings become chilly, 

 many species of flies retire into houses and swarm in 

 the windows : that at first they are very brisk and alert; 

 but, as they grow more torpid, that they move with dif- 

 ficulty, and are scarcely able to lift their legs, which 

 seem as if glued to the glass ; and that by degrees many 

 do actually stick till they die in the place. Then noti- 

 cing Dr. Derham's opinion as just stated, he further re- 

 marks, that they easily overcome the atmospheric pres- 

 sure when they are brisk and alert. But, he proceeds, 

 in the decline of the year this resistance becomes too 

 mighty for their diminished strength ; and we see flies 

 labouring along, and lugging their feet in windows as if 

 they stuck fast to the glass b . 



Sir Joseph Banks, to whom every branch of Natural 

 History becomes daily more indebted, has lately excited 

 an inquiry, the results of which have confirmed Derham's 

 system concerning this motion of animals against gravity. 

 When abroad, he had noticed that a lizard, on account 



a Physico-Theol. Ed. 13. 363, note b. 

 b Nat. Hist. 11. 274. 



