324 MOTIONS OF INSECTS. 
mere fancies, since they can walk as well upon the clean- 
est glass as upon the most tarnished. Reaumur also at- 
tributes this faculty of these animals to the hairs upon 
their suckers*. That learned and pious naturalist, Dr. 
Derham, seems to have been one of the first who gave 
the true solution of this enigma. “ Flies,” says he, ‘‘ be- 
sides their sharp hooked nails, have also skinny palms 
to their feet, to enable them to stick on glass and other 
smooth bedies, by the pressure of the atmosphere’.” He 
compares these palms to the curious suckers of male Dy- 
tisct, 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 so- 
lution. He observes that in the decline of the year, when 7 
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 difficulty, 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 noticing Dr. Derham’s 
opinion as just stated, he further remarks, that they easily 
overcome the atmospheric pressure 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°. 
Sir Joseph Banks, to whom every branch of Natural 
2 iy. 259, > Physico-Theol. Ed. 13. 363, note &. 
© Nat, Hist. ii. 274. 
