218 THE ECONOMIC IMPORTANCE OF ANIMALS 



poisons they manufacture, into the blood. This causes the chill 

 followed by the fever so characteristic of malaria. The spores 

 may again enter the blood corpuscles and in forty-eight or 

 seventy-two hours repeat 'the process thus described, depending 

 on the kind of malaria they cause. The only cure for the 

 disease is quinine in rather large doses. This kills the parasites 

 in the blood. But quinine should not be taken except under 

 a physician's directions. 



The Malarial Mosquito. Fortunately for mankind, not all 

 mosquitoes harbor the parasite which causes malaria. The harm- 

 less mosquito (culex) may be usually distinguished from the 

 mosquito which carries malaria (anopheles) by the position taken 



How to distinguish the harmless mosquito (culex), a, from the malarial mosquito 

 (anopheles'), b, when at rest. Notice the position of legs and body. 



when at rest. Culex lays eggs in tiny rafts of one hundred or more 

 eggs in any standing water ; thus the eggs are distinguished from 

 those of anopheles, which are not in rafts. Rain barrels, gutters, 

 or old cans may breed in a short time enough mosquitoes to stock 

 a neighborhood. The larvae are known as wigglers. They breathe 

 through a tube in the posterior end of the body, and may be rec- 

 ognized by their peculiar movement when on their way to the sur- 

 face to breathe. The pupa, distinguished by a large thoracic 

 region, breathes through a pair of tubes on the thorax. The fact 

 that both larvae and pupae take air from the surface of the water 

 makes it possible to kill the mosquito during these stages by pour- 

 ing oil on the surface of the water where they breed. The intro- 

 duction of minnows, gold fish, or other small fish which feed 



