THE PROTOZOA 143 



The next thing, then, is to see how the mosquito becomes infected. 

 The female mosquito lives by sucking the warm blood of mammals, 

 including man, and in order to do this is furnished with a very 

 complex instrument, the proboscis. This is composed of seven 

 distinct parts, all modified from the structures which in other insects 

 constitute the jaws and accessory organs, and together they form a 

 most efficient piercing stylet, as we soon learn to our discomfiture 

 when we go into a mosquito-infected district. Such an apparatus 

 is absent in the male, which cannot, therefore, suck blood. Not 

 only does it form a piercing organ, but it is so constructed that when 

 it reaches a small blood-vessel the parts can be closed together and 

 form a tube leading to the mouth. Behind the mouth is a suctorial 

 pharynx, by means of which a quantity of blood is drawn up into the 

 stomach of the mosquito. Should the female stab a person infected 

 with malaria it automatically sucks up with the blood, corpuscles 

 containing the parasites in different phases of development. In the 

 stomach all stages of the parasite are digested with the blood save 

 only the gametocytes, and these are not merely left undigested, but 

 actually stimulated to activity and assume a motile amoeboid form. 

 In this country we have a species closely related to the mosquito 

 Anopheles, namely, the gnat Culex pipiens, also capable of stinging 

 human beings. C. pipiens is the intermediary in a malaria fever, 

 avian malaria, confined entirely to birds. So marvellously exact 

 is the inter-relationship between the parasite and its hosts that on the 

 one hand the gnat cannot be infected with human malaria or ague, 

 nor on the other hand can the mosquito carry avian malaria, 

 although the parasites in the two cases are practically identical in 

 appearance and life history. Each species is capable of spreading 

 only the particular disease that affects either the man or the bird. 



Still within the stomach of the mosquito the nucleus of the 

 macrogametocyte undergoes an unequal division, and the smaller 

 daughter nucleus surrounded by a minute quantity of protoplasm 

 is extruded from the cell as the so-called " polar body." After 

 this process of maturation, or ripening, the cell is ready for fertilisa- 

 tion, and so is now a macrogamete. 



The changes in the (microgamejgTare more complex. Its nucleus 

 enlarges, and after the cell has" passed through a short phase of 

 activity, putting forth and withdrawing pseudopodia, it breaks up 

 by a kind of multiple fission into six or eight masses. Each of these 

 consists of a karyosome surrounded by chromatin granules. They 

 take up a position near the periphery of the protoplasm, which gives 

 rise to usually six long actively moving filiform processes. Into 

 each of these a karyosome migrates, occupying a central position, 

 while its attendant chromatin grains are scattered along its length. 



