220 LIFE IN THE INSECT WORLD. 



it, and having thus dissolved the desirable mor- 

 sel, sucks it up without difficulty. 



Many insects, you know, can walk upon glass 

 and other smooth surfaces with perfect ease and 

 security, even with their backs downwards. 

 The house-fly is enabled to do this by means of 

 an apparatus in the feet, which I will endeavor 

 to describe to you. 



No doubt yon have sometimes amused your- 

 selves with making a thimble cling to your arm 

 or lip by sucking the air from it ; you were 

 aware that this effect would be produced, al- 

 though you may not have understood the cause. 

 The inside of the thimble being deprived of air, 

 that which was without pressed upon it with 

 such force as to cause it to remain in its position, 

 and adhere to the flesh. It is precisely upon this 

 principle that the house-fly walks upon glass, or 

 upon the ceiling, without danger of slipping or 

 falling. 



Each of the feet is furnished with two claws, 

 and at the base of these are two suckers or 

 membranes, connected with the feet by a fun- 

 nel-shaped neck, which is capable of being 

 moved in every direction. These suckers can 



