PROTOZOA IN THE CIRCULATORY SYSTEM 85 



These merozoites will, if not ingested by leucocytes, enter 

 again and repeat the schizogony in erythrocytes. After re- 

 peated and simultaneous schizogony in geometric progres- 

 sion, a large number of infected erythrocytes will be 

 destroyed, setting free an ever-increasing amount of toxic 

 substance. The onset of the malarial chill and fever corre- 

 sponds with the time of liberation of merozoites. 



Some of the merozoites develop into gametocytes instead 

 of schizonts in ervthrocvtes (Fig. 21, '^-l^). When fully 

 formed thev can be differentiated into macro- and micro- 

 gametocytes, but remain as such while in the human blood. 

 When a female anopheline mosquito sucks blood contain- 

 ing the gametocytes, microgametocytes develop into micro- 

 gametes (Fig. 21, 10, 11) and macrogametocytes into macro- 

 gametes (Fig. 21, 8, 12) ii^ the stomach. An ookinete is 

 formed when a microgamete fuses with a macrogamete 

 (Fig. 21, 1-. 13). The ookinetes are mobile, penetrate 

 through the stomach wall, and become rounded into 



Description of Fig. 21 



1. A sporozoite entering human blood. 



2. Sporozoite entering an erythrocyte. 



3. Young schizont. 

 4-6. Schizogony. 



7, 8. Macrogametocytes. 

 9, 10. Microgametocytes. 



11. Microgamete-formation in the stomach of a mosquito. 



12. Union of gametes. 



13. Zygote or ookinete. 



14. Young oocyst. 



15. Oocyst in which sporozoites are developing. 



16. Mature oocyst from which sporozoites are emerging. 



17. Sporozoites entering the salivary gland. 



