THE MALARIAL PARASITE 181 



melanin granules in the cytoplasm. In the microgametocyte 

 the granules are generally more evenly distributed; in the 

 macrogametocyte they are aggregated round the nucleus. In 

 P. vivax and P. malaricz the gametocytes are rounded in shape 

 (fig. 38, $ and ? ) and are not very easily distinguished from 

 the younger stages of the trophozoite, but in P. immaculatum 

 they are readily recognisable because they assume a crescentic 

 form, the convexity of the crescent being closely applied to 

 one side of the corpuscle (fig. 39, A $ and ? ). Though game- 

 tocytes are found in large numbers in the peripheral circula- 

 tion of malarial patients and can easily be obtained by drawing 

 blood from a finger, they are incapable of further development 

 in the human system, and if they are not transferred to the 

 intermediate host they eventually perish. But if the patient 

 is bitten by a mosquito of the genus Anopheles all stages of 

 the parasite, ring-shaped, amoeboid, schizonts and crescents, 

 are drawn up with the blood into the stomach of the insect, 

 and it is a noteworthy fact that all are promptly digested ex- 

 cept the gametocytes. These last are not only resistant to 

 the action of the digestive juices, but appear to be stimulated 

 to further development. 



The macrogametocyte does not alter much. If it is a 

 crescent form of pernicious malaria, it frees itself from the 

 remnants of the corpuscle in which it was enclosed, assumes 

 a rounded form, and its nucleus divides into two unequal 

 portions. The smaller portion, surrounded by a small invest- 

 ment of cytoplasm, is extruded as a polar body (fig. 39, 

 B and (7), and when this process is completed the macro- 

 gametocyte has become a macrogamete, ready for fertilisation. 



The development of the microgametocyte is more com- 

 plicated. It becomes spherical and its previously round 

 nucleus assumes an oval shape. At first it is motionless, but 

 suddenly it contracts and the cytoplasm and melanin granules 

 contained in it execute rapid streaming movements. After 

 a few seconds pseudopodial processes are thrust out from 

 various points of the surface, to be withdrawn again and re- 

 appear in another place. At this time some of the melanin 

 granules are often cast out of the body. The pseudopodial 

 movements cease for a few seconds and then suddenly some 

 four to eight, most usually six, long slender hyaline processes 

 are thrust out from as many points of the surface, and as soon 



