06 THE PHILOSOPHY 



is certain that their fenfe of feeing is acute ; and we know 

 that they are amply fupplied with nerves, wliich produce 

 the fame effe<Sts as the brain in larger animals. If they are 

 deprived of noftrils, the flighteft attention muft convince us, 

 that fome of them poffefs the {enie of fmelling in a very high 

 degree. Upon any other fuppofition, how fliould the dif- 

 ferent fpecies of flies, the moment they efcape from the 

 chryfalis ftate, diflinguifh, and diredtly approach, the differ- 

 ent animal and vegetable fubftances Nature has deftined for 

 their refpe(Slive nourifhment ? A piece of meat is no fooner 

 expcfed to the air than it is covered with flefli flies, upon 

 which they both feed and depoflt their eggs. Without this 

 fenfe, how fhould wafps, and other flies, be allured from 

 coniiderable diftances into bottles encrufted with honey or 

 molafl^es ? Thefe, and fimilar actions, cannot be effects of 

 fight *, for the diftance, the minutenefs, and frequently the 

 poiition of the food, render it irapoflible for the eye to dif- 

 cover thofe fubfliances to which they inftantly refort. 



With regard to hearing, it is more difiicult to determine 

 whether infe<Sl:s be endowed with this fenfe. We can judge 

 of it, not by the knife of the Anatomift, but by the affections 

 and motions of the animals themfelves. Several trials I have 

 made on houfe-flies incHne me to think that thefe animals 

 poffefs a fenfe of a nature fimilar, at Icaft, to that of hearing. 

 At the diflance of three or four feet, a fmart flroke, even 

 upon a flone wall, alarms and puts them to flight. But this 

 may partly be attributed to the vibration in the wall, or the 

 concufhon of the air, produced by the flroke. To obviate 

 this difiiculty, at the fame difl:ance of between three and 

 four feet, I ftruck the air repeatedly with a bookbinder's 

 folder, without giving the fmallefl alarm ^o the flies. But, 

 when I flruck the folder againfl the boards of a book, which 

 I held in my hand, and made a fmart noife, the animals 

 were inftantly alarmed, and flew off at the fecond ftrokeo 



