THE HOUSE FLY 75 



body? Do you know of any use to which they may be 

 put by the fly ? They are called balancers. What organ in 

 the other insects do they take the place of? 



Make a drawing of the wing (X4)- 



Remove -the balancer, put it under low power of micro- 

 scope, and draw. 



(3) Remove one of the legs from the body. How many 

 segments? Remove the tarsus and put it under the low 

 power of the microscope. Note the two hooks and the pads. 

 Study the structure closely. The pads are called pulvilli and 

 are used to secrete a sticky fluid by means of which the fly 

 adheres to smooth surfaces or to the ceiling. 



Draw the tarsus. 



Draw dorsal view of fly (X2). 



The fly belongs to the order Diptera, a group of insects 

 having two wings. 



Development. — (i) The eggs of the fly are laid in 

 decaying waste matter and after a short time the larva, a 

 headless, footless maggot is hatched. Like other larvae 

 it eats ravenously for a few days, molts several times, and 

 finally assumes a tough brown covering which is the crys- 

 alis of the pupa state. 



After remaining about a week in the pupa state it emerges 

 as a full grown imago. 



(2) It is an easy matter to raise house flies and watch 

 their metamorphosis. 



Draw larva and pupa (X4)- 



Habits. — Flies are scavengers and are therefore of the 

 greatest benefit in the economy of nature. Why is this? 

 It is also suspected that flies carry and distribute the germs 

 of typhoid fever, and that mosquitoes carry and distribute 



