226 



})nblished by him in the Annals of Natural History and 

 Science (1845). 



Firstly — Insects capable of walking up glass, lose that power 

 after their feet have been subjected to finely pulverised nitrate 

 of silver. This destroys the hairs, and deprives the bosses of 

 their viscid secretion. It would not do so were the hairs per- 

 fectly dry. 



Secondly — An insect cannot walk on glass against gravity 

 when its feet are choked by finely powdered starch or any other 

 substance. When they have cleaned their feet they are able to 

 walk on smooth surfaces as usual. 



Thirdly — ^When they are unable to walk up a perfectly clean 

 glass jar, they can do so when it is breathed upon or slightly 

 soiled. 



Fourthly — The visible tracks of the insects may be detected 

 on glass. 



Lastly — These creatures have been found to walk up plane 

 perpendicular surfaces with as great ease in the vacuum of an 

 air pump as in the open air ; as atmospheric pressure cannot 

 exist there, we must designate this as the experimentum crucis. 



How singularly correct must now seem the first account 

 of the foot of the fly written by Dr. Power two hundred years 

 ago (and quoted by the author of the Episodes of Insect Life), 

 compared with the more elaborate explanations of Sir Everard 

 Home and others. Dr, P. says, " Speaking of Musca domes- 

 tica, her other four feet are cloven, and armed with little claws 

 by which she fastens on rugosities and asperities of all bodies 

 like a catamount. She is also furnished with a kind of fuzzy 

 substance like little sponges, with which nature has lined the 

 soles of her feet, which substance is also repleated with a 

 white viscous liquid, squeezed out at pleasure to glew herself 

 to the surface." 



We must now examine how far we have other analogies cor- 

 roborative to the assertion, that it is by viscosity alone that 

 insects, etc., adhere to plane perpendicular surfaces. We shall 



