CH. IX] LIFE-CYCLE OF MALARIAL PARASITE I3I 



is capable of entering another red cell and repeating the above-described 

 cycle. 8-11. Formation of the gametocytes ; these arise by growth of 

 merozoites and after reaching a certain size (10) develop into either male 

 or female gametocytes (iia and iifc) ; in the male gametocyte (116) the 

 nucleus is larger and more scattered than in the female (iia). 



12-16. Stages of the sexual generation in the stomach of the 

 mosquito. 12a, 13(1 and 14a. The formation of the female gamete. 126, 

 136 and 146. Stages in the formation of the male gametes. 15. Fertiliza- 

 tion, resulting in the formation of a zygote (16), which then becomes 

 motile and is known as the ookinete (17). 



iS-22. Stages in the sporogonous cycle in the mosquito. The 

 ookinete (17) bores into the stomach wall and forms a cyst (iS) ; it 

 increases in size, its nucleus multiplies and eventually each nucleus 

 becomes surrounded by a mass of cytoplasm, forming a number of sporo- 

 blasts (19) ; each of these sporoblasts gives rise to numerous sporozoites 

 (20-21). The ripe sporocyst is represented in 21, and the escaping 

 sporozoites (22) enter the salivary gland of the mosquito and escaping 

 with the salivary secretion, enter the blood and are capable of repeating 

 the cycle. 



the process of schizogony. These are the sexual forms, and 

 are of two kinds, male and female. It is probable that the 

 merozoites differentiate sexually at an early stage of the disease, 

 but what determines the sex is unknown. 



In its earliest stages the young sexual form is indistinguish- 

 able from an ordinary trophozoite, but it grows extremely 

 slowly and never assumes the ring form. 



As it grows its cytoplasm becomes filled with granules of 

 pigment and soon certain differences can be noticed in the 

 staining reactions of the protoplasm, resulting in the differentia- 

 tion of what are known as the macrogametocytes and micro- 

 gametocytes respectively. The former are destined to give 

 rise to the female gametes, and are characterized by the pos- 

 session of a small feebly-chromatic nucleus and a dense cyto- 

 plasm containing numerous granules and much pigment. The 

 microgametocytes, which give rise to the male gametes, have 

 each a large densely chromatic nucleus extending across the 

 middle of the cell, and the cytoplasm is clearer and contains 

 less pigment. 



When full grown, the sexual forms are larger than the red 

 cells which contain them ; consequently the latter are consider- 

 ably distorted by the parasite and form conspicuous objects 

 that were noticed long before their true nature was recognized. 



9—2 



