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different from that of Culex or Aëdes. Its most distinc- tive character is in the shape of the respiratory tubes, which are very broad at the ends. The parasitë of malaria is hot a bacterium but a micro- scopic protozoan animal named P/asmodium. There are several species or varieties that correspond with the difl'er- 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 lire in the red corpus- cles of the [lood. 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, de»'elop there into males and females. In the stomach of the mosquito, these sexual individuals unite in pairs, and the resulting z, ygotes, as they are called, penetrate into the cells of the stomach walf. Here they lire for a while and multiply into a great number of sma[l spindle-shaped creatures, which go through the stomach wall into the body cavity of the mosquito and at last col- lect in the salivary glam{s. If now the mosquito, with its salivary glands full of the Plasnodium parasites in this stage, bites some other animal, the parasites are almost sure to be injected into the wound with the salira. If they are hot at once destroved by the white blood cor- pus'cles, they will quickly enter the red blood corpuscles, and the victim will soon show symptoms of malaria. THE HOUSE FL." AND SOME OF lrs RELATIONS Our familiar domestic pest, the bouse 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, 3luc domeIic, the bouse f]v--musc being the Latin word for fly. The bouse f]y (Fig. 82 A), though particularly a domes-

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