196 THE INTEGUMENTAL SKELETON OF THE IMAGO. 



kinde of substance like little sponges, with which she hath lined 

 the soles of her feet, which substance is always repleated with 

 a whitish, viscous liquor, which she can at pleasure squeeze 

 out, and so sodder and be-glew herself to the plain she walks 

 on, which otherways her gravity would hinder' (p. 5). 



This statement of Power's was subsequently controverted by 

 Leeuwenhoek [84], who supposed that the minute hairs on the 

 pads have a hold even on the polished surface of glass, and act 

 as tenterhooks ; whilst Dereham [86] suggested that the pads 

 act as suckers, and that the insect is supported by atmospheric 

 pressure. This view has been the popular one ever since, but 

 Blackwall* and Inman [87] reverted to Power's original sugges- 

 tion, which is certainly the correct one. 



The minute size of the papilla; and setae on the under 

 surface of the pads formerly made their investigation exceed- 

 ingly difficult, but the great similarity of these to the so-called 

 suckers of Dytiscus, and the pulvilli of the Harpalidse, has 

 long been recognised. Tuffen West [88] compared the pads of 

 the Diptera with the pulvilli of the Coleoptera, and gives 

 a large number of beautiful and elaborate figures of the 

 pads of various insects, which are most accurate in all their 

 details. West supposed that the separate seta; act as suckers. 

 In 1871 I showed at the Royal Microscopical Society that the 

 great water-beetle remains suspended by its so-called suckers 

 in a very perfect air-pump vacuum [89]. Flies also walk 

 perfectly well over the exhausted dome of an air-pump. 

 Gilbert White, in his ' Natural History of Selborne,' records 

 some interesting observations which he made on flies in 

 autumn, when they are feeble. He states that they often 

 struggle to remove their feet from glass as if they were firmly 

 glued to its surface. In my former work on the Blow-fly [62], 

 I made the following statements, which still represent my views 

 on this subject : 



' There is no essential difference in the pads of flies and the 

 pulvilli of beetles, moths, and other insects ; a similar fluid is 



* ' Remarks on the Pulvilli of Insects.' Trans. Linn. Soc, Lond., vol. xvi., 

 p. 767. 1883. 



