INSECTS I THEIB FEET. 109 



CHAPTER VII. 



INSECTS I THEIR FEET. 



I HAVE here inclosed a small window-fly in the live -box of 

 the microscope, that you may examine the structure of its 

 feet as it presses them against the glass cover ; and thus 

 not only get a glimpse of an exquisitely-formed structure, 

 but acquire some correct ideas on the question of how a 

 fly is enabled to defy all the laws of physics, and to walk 

 jauntily about on the under surface of polished bodies, 

 such as glass, without falling, or apparently the fear of 

 falling. And a personal examination is the more desirable 

 because of the hasty and erroneous notions that have been 

 promulgated on the matter, and that are constantly dis- 

 seminated by a herd of popular compilers, who profess to 

 teach science by gathering up and retailing the opinions 

 of others, often without the slightest knowledge whether 

 what they are reporting is true or false. 



The customary explanation has been that given by Der- 

 ham in his " Physico- theology " ; that " divers flies and 

 other insects, besides their sharp-hooked nails, have also 

 skinny palms to their feet, to enable them to stick to glass, 

 and other smooth bodies, by means of the pressure of the 

 atmosphere, after the manner as I have seen boys carry 

 heavy stones, with only a wet piece of leather clapped on 

 the top of a stone." Bingley, citing this opinion, adds 

 that they are able easily to overcome the pressure of the 

 air "in warm weather, when they are brisk and alert; 

 but towards the end of the year this resistance becomes 

 too mighty for their diminished strength ; and we see flies 



