THE PROTOZOA 



137 



There are a hundred and twenty-five species of mosquitoes in North 

 America, but it is only the female of the genus Anopheles which can 

 transmit malaria to man, though some members of the genus Culex do 

 transmit it to birds. (At least this is true in India.) 



The distinguishing characteristics of the two groups is as follows 

 (Fig. 51) : In Culex the wings are clear, while in Anopheles they have 



Fig. 51. 



A. Life history of house mosquito (Culex). 



B. Life history of malaria mosquito (Ano- 

 pheles). (From Howard, U. S. Dept. of Agri- 

 culture). 



C. Culex larva, showing details of external 

 structure. (After Riley and Johannsen.) 



brown spots. In Culex the axis of the body forms a curved line as 

 though the insect were hump-backed, while Anopheles presents a 

 straight line when resting. For those familiar with insect anatomy we 

 may add that Culex has short maxillary palpi while Anopheles has them 

 almost as long as its proboscis ; and lastly, for those with a musical ear, 

 we may add that the female Anopheles, which is the only one which 

 carries the malarial parasite, sings several tones lower than the Culex. 



The eggs of Culex are always laid in a mass, while those of 

 Anopheles are laid singly. As the eggs hatch, the larvae of Culex hang 

 from the surface of the water at about an angle of 45 degrees, while the 

 larvae of Anopheles lie almost parallel to the surface of the water. 



Prevention is always the scientific method of overcoming disease. 

 Because mosquitoes lay their eggs in quiet pools, men conceived the 

 idea of preventing these eggs from hatching. This has not been possi- 

 ble, but oil poured on the water will kill the little wrigglers after they 

 hatch. 



The breathing tubes of wrigglers are provided with hydrofuge 

 plates at their openings which will not permit water to enter. Since 

 these hydrofuge surfaces are due to the presence of oil, it is obvious that 

 oil poured on the surface of the water will mix with this and cause the 



