THE MOSQUITO THEORY 381 



into the flagellated body. This transformation occurred in a pro- 

 portion of instances very much greater than occurs in malarial 

 blood spread in the ordinary way on a slide and exposed to the air. 

 He found, also, that the flagella broke away from the flagellated 

 body, yet he was unable to trace what became of the free flagella. But 

 in a "dapple-winged" mosquito (anopheles) fed in the same way 

 with malarial blood containing crescents (summer-autumn fever), 

 he discovered, embedded in the tissues of the stomach wall, certain 

 peculiar oval cells containing the same pigment as the malarial 

 parasite in the human blood. This was, in fact, the extra-corporeal 

 form of the human parasite after impregnation, namely, the zygote. 

 Next he discovered pigmented cells in the body tissues of mosquitoes 

 fed upon sparrows' blood, affected with a similar parasitical condition 

 to malaria (proteosoma) ; and from one step to another he demon- 

 strated the evolution of the mosquito phase of these parasites. 

 Eoss made it evident that the cycle of extra-corporeal development 

 of the parasite, as we have already seen, is carried on inside the 

 body of the mosquito. After malarial blood is shed or swallowed 

 by the mosquito, the changes already described take place. Practi- 

 cally, all the crescents become spheres within a few minutes of being 

 taken into the stomach of the mosquito, then the male gametes 

 become flagellated, and the female gametes become impregnated. 

 According to Eoss, the condition which brings about the transfor- 

 mation of crescents into flagellated bodies is not low temperature, 

 nor exposure to air, nor contact with the wall of the mosquito's 

 stomach, but abstraction of the water from the serum of the blood. 



However that may be, the changes resulting from impregnation 

 result in the mosquito's stomach in the production of the zygote or 

 fertilised cell. This body is a travelling vermicule, and on or about 

 the second day it penetrates the stomach wall and becomes encysted 

 between the muscle fibres. The number of zygotes produced in the 

 mosquito after its feed on malarial blood varies widely, sometimes 

 being few, sometimes many. In the enlarging encysted cell there 

 now come to be developed a number of cells known as zygotomeres, 

 which as development proceeds become blastophores filled with 

 filiform spore cells (sporozoits or germinal rods or zygotoblasts). 

 Ultimately, the zygote becomes thus transformed into a cyst (sporo- 

 cyst) packed full of zygotoblasts. When fully developed, at about 

 the eighth or ninth day after the mosquito ingested the malarial blood, 

 the sporocyst measures about 60 micromillimetres in diameter. 

 About the twelfth day it bursts, discharging the zygotoblasts, which 

 are, of course, " spores " or reproductive elements, into the body cavity 

 and fluid of the mosquito, and spreading from thence they become 

 accumulated in the large veneno-salivary gland, and are thus in a 

 position to be injected along with its secretion into the human 



