MOTIONS OF INSECTS. 491 



K. Ms.).^ In two other genera of the same order, Silpha and Cicindela, 

 the anterior tarsi of the males are furnished with them ; in these, there- 

 fore, they may be regarded, like the suckers of the larger water-beetles 

 {Dytisci), as given for sexual purposes.^ The three first joints of the 

 anterior tarsi of many of the larger rove-beetles (^Staphylinus L.) are 

 dilated so as to form, as in the last-mentioned insects, an orbicular patella, 

 but covered by cushions. Since in them this is not peculiar to the males, 

 it is probably given that they may be able to support their long bodies 

 when climbing. 



But the most remarkable class of climbers consists of those that are 

 furnished with an apparatus by which they can form a vacuum, so as to 

 adhere to the plane on which they are moving by atmospheric pressure. 

 That flies can walk upon glass placed vertically, and in general against 

 gravity, has long been a source of wonder and inquiry ; and various have 

 been the opinions of scientific men upon the subject. Some imagined that 

 the suckers on the feet of these animals were sponges filled with a kind of 

 gluten, by which they were enabled to adhere to such surfaces. This 

 idea, though incorrect, was not so absurd as at first it may seem ; since 

 we have seen above in many instances, and very lately in that of the 

 Sminthunis fuscus, that insects are often aided in their motions by a secre- 

 tion of this kind. Hooke appears to have been one of the first who 

 remarked that the suspension of these animals was produced by some 

 mechanical contrivance in their feet. Observing that the claws alone could 

 not effect this purpose, he justly concluded that it must be principally 

 owing to the mechanism of the two palms, pattens, or soles, as he calls 

 the suckers ; these he describes as beset underneath with small bristles or 

 tenters, like the wire teeth of a card for working wool, which having a 

 contrary direction to the claws, and both pulling difl^erent ways, if there 

 be any irregularity or yielding in the surface of a body, enable the fly to 

 suspend itself very firmly. That they walk upon glass he ascribes to 

 some ruggedness in the surface ; and principally to a smoky tarnish which 

 adheres to it, by means of which the fly gets footing upon it."^ But these 

 tenter-hooks in the suckers of flies, and this smoky tarnish upon glass, are 

 mere fancies, since they can walk as well upon the cleanest glass as upon 

 the most tarnished. Reaumur also attributes 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, " besides their sharped hooked nails, have 

 also skinny palms to their feet, to enable them to stick on glass and other 

 smooth bodies, by the pressure of the atmosphere.''^ He compares these 

 palms to the curious suckers of male Di/tisci, 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 excel- 

 lent 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; 



» The insect here alliuled to is figured by Olivier under the name of Tenebrio nitens (No. 

 57. t. i. f. 4.) : his Helops aneus {No. 58. I. i. f. 7.) is a different inxect. 



' See Kirby, in Fauna Bireali- Americana, oa various modifications of these foot cushions 

 amonsst .some iribes of beetles. 



=• Mkrogr. 170. * iv. 259. » Physico-Theol. ed. 13. 363. note b. 



