OF NATURAL HISTORY. 87 



guifh, and diredly approach, the different animal and vegetable 

 fubftances Nature has deftined for their refpedtive nourifhment ? A 

 piece of meat is no fooner expofed to the air than it is covered with 

 fleflb flies, upon which they both feed and depofit their eggs. With- 

 out this fenfe, how fliould wafps, and other flies, be allured from 

 confiderable diftances into bottles encrufted with honey or molafl!es ? 

 Thefe, and fimilar aftions, cannot be effeds of fight ; for the di- 

 ftance, the minutenefs, and frequently the pofition of the food, ren- 

 der it impofllble for the eye to difcover thofe fubftances to which 

 they inftantly refort. 



With regard to hearing, it is more difficult to determine whether 

 infe6ts 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 in- 

 cline me to think that thefe animals poflefs a fenfe of a nature fimi- 

 lar, at leaft, to that of hearing. At the diftance of three or four 

 feet, a fmart fliroke, even upon a ftone wall, alarms and puts them 

 to flight. But this may partly be attributed to the vibration in the 

 wall,, or the concuflTion of the air, produced by the ftroke. To ob- 

 viate this, difficulty, at the fame diftance of between three and four 

 feet, I ftruck the air repeatedly with a bookbinder's folder, without 

 giving the fmaileft alarm to the flies. But, when I ftruck the fol- 

 der againft 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 ftroke. The fame effedt is produced in a room 

 juft light enough to render the animals vifible. Thefe trials,, which 

 I have often repeated, feem to indicate that flies, if they are really 

 deprived of ears, are endowed with an analogous feufe, though we 

 are ignorant of its fituation. 



Natui^lifts. 



