It was found that when blood containing these sexual forms was sucked up by an Anopheline mosquito and taken into its stomach, a microgamete penetrated and fertilized a macrogamete in a way analogous to what takes place in the fertilization of the egg in higher forms. The resultant, mobile organism is known as the _migratory ookinete_. In this stage the parasite bores through the epithelial lining of the "stomach" (mid-intestine) of the mosquito and becomes encysted under the muscle layers. Here the _oocyst_, as it is now known, matures and breaks up into the body cavity and finally its products come to lie in the salivary glands of the mosquito. Ten to twelve days are required for these changes, after which the mosquito is infective, capable of introducing the parasite with its saliva, when feeding upon a healthy person. Thus the malarial parasite is known to have a double cycle, an alternation of generations, of which the asexual stage is undergone in man, the sexual in certain species of mosquitoes. The mosquito is therefore the definitive host rather than the _intermediate_, as usually stated. The complicated cycle may be made clearer by the diagram of Miss Stryke (1912) which, by means of a double-headed mosquito (fig. 126) endeavors to show how infection takes place through the biting of the human victim, (at A), in whom asexual multiplication then takes place, and how the sexual stages, taken up at B in the diagram, are passed in the body of the mosquito. [Illustration: 126. Life cycle of the malarial parasite. After Miss Anna Stryke.] The experimental proof that mosquitoes of the Anopheline group are necessary agents in the transmission of malaria was afforded in 1900 when two English physicians, Drs. Sambon and Low lived for the three most malarial months in the midst of the Roman Campagna, a region famous for centuries as a hot-bed of malaria. The two experimenters moved about freely throughout the day, exposed themselves to rains and all kinds of weather, drank marsh water, slept exposed to the marsh air, and, in short, did everything which was supposed to cause malaria, except that they protected themselves thoroughly from mosquito bites, retiring at sunset to a mosquito-proof hut. Though they took no quinine and all of their neighbors suffered from malaria, they were absolutely free from the disease. To complete the proof, mosquitoes which had fed in Rome on malarious patients were sent to England and allowed to bite two volunteers, one of them Dr. Manson's own son, who had not been otherwise exposed to the disease. Both of these gentlemen contracted typical cases of malaria and the parasites were to be found in abundance in their blood. [Illustration: 127. Eggs of Anopheles. After Howard.] Since that time there have been many practical demonstrations of the fact that malaria is transmitted exclusively by the bite of mosquitoes and that the destruction of the mosquitoes means the elimination of the disease.