26 TROPICAL MEDICINE AND HYGIENE 



forms, are examined closely, it will be seen that in some 

 there is a space free from pigment in the centre of the 

 clump of pigment ; these are the female forms. In the 

 others there is no such clear space, and the pigment 

 clump is larger and less regular. These are the male 

 forms (fig. 8, x l ). 



If watched for a time varying with different cases, 

 and in the same case on different occasions, the game- 

 tocytes are seen to become actively sexual. The first 

 change in both is that the parasites become shorter and 

 broader, first ovoid and finally circular or spheroidal. 

 This is spoken of as the " transformation " of the 

 crescents. The remnants of the red corpuscle disappear. 

 One or two small refractile globules, the polar bodies, 

 are extruded, and there is much agitation of the pigment. 



The females macrogametes unless fertilized undergo 

 no further change (fig. 8, y, z). The males flagellate and 

 the flagella " microgametes " ultimately separate from the 

 residual protoplasm which contains aH the pigment and 

 swim about freely in the blood plasma (fig. 8, y 1 , z l ). 

 They have been seen to enter and fertilize the female or 

 macrogamete. This is the first stage in the sexual cycle 

 of the malaria parasites. The macrogamete when fertilized 

 is a zygote, i.e., the product of conjugation. . . . This 

 zygote is actively motile, creeping and moving like a 

 gregarine. It is at this stage known as the travelling 

 vermicule or ookinet. In the coccidia, it may be remem- 

 bered, the zygote is non-motile and is called the " oocysL" 

 The further changes in the zygote, by which the contents 

 ultimately divide into a mass of minute thread-like bodies, 

 the sporozoites, takes place in the stomach wall of the mos- 

 quito between the epithelial and musculo-membranous 

 layers (fig. 9). This series of events is known as the sexual, 

 exogenous, or mosquito cycle, and by parasitologists as 

 sporogony. The sporozoites ultimately, in eight days or 

 more according to the temperature, accumulate in cells in 

 the salivary glands of the mosquito and are injected with 

 the saliva of that insect into man. After this, in about 



