INSECTS
different from that of Culex or Aëdes. Its most distinctive character is in the shape of the respiratory tubes, which are very broad at the ends.
The parasitë of malaria is not a bacterium but a microscopic protozoan animal named Plasmodium. There are several species or varieties that correspond with the different 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 corpuscles of the blood. Here they multiply by asexual reproduction, producing for a while many other asexual generations. 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 lire 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 collect 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 destroved by the white blood corpuscles, they will quickly 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 particularly a domes-
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