INSECTS 



different from that of Culex or Aedes. Its most distinc- 

 tive character is in the shape of the respiratory tubes, 

 which are very broad at the ends. 



The parasite of malaria is not a bacterium but a micro- 

 scopic protozoan animal named Plasmodium. There are 

 several species or varieties that correspond with the differ- 

 ent varieties of the disease. The malaria Plasmodium has 

 a complicated life cycle and is able to complete its life only 

 when it can spend a part of it in the body of a mosquito 

 and the other part in some vertebrate animal. In the 

 human body the malaria parasites live in the red corpus- 

 cles of the blood. Here they multiply by asexual repro- 

 duction, producing for a while many other asexual gener- 

 ations. Eventually, however, certain individuals are 

 formed that, if taken into the stomach of an Anopheles 

 mosquito, develop there into males and females. In the 

 stomach of the mosquito, these sexual individuals unite 

 in pairs, and the resulting zygotes, as they are called, 

 penetrate into the cells of the stomach wall. Here they 

 live for a while and multiply into a great number of small 

 spindle-shaped creatures, which go through the stomach 

 wall into the body cavity of the mosquito and at last col- 

 lect in the salivary glands. If now the mosquito, with its 

 salivary glands full of the Plasmodium parasites in this 

 stage, bites some other animal, the parasites are almost 

 sure to be injected into the wound with the saliva. If 

 they are not at once destroyed by the white blood cor- 

 puscles, they will quick] v enter the red blood corpuscles, 

 and the victim will soon show symptoms of malaria. 



The House Fly and Some of Its Relations 



Our familiar domestic pest, the house fly, may be taken 

 as the type of a large group of flies, and in particular of 

 those belonging to the family Muscidae, which is named 

 from its best known member, Musca domestica, the house 

 fly — musca being the Latin word for fly. 



The house fly (Fig- 182 A), though particularlv a domes- 



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