PLASMODIUM 



59 



divided so as to produce small nuclei normally about six in number. 

 The cytoplasm now becomes rapidly extended outwards into about six 

 long slender threads into each of which there passes one of the small 

 nuclei also elongated, almost .threadlike, in form. These protoplasmic 

 threads lash about violently like so many fiagella, eventually tear them- 

 selves free from the central mass of cytoplasm — which then degenerates 

 — and swim off actively through the fluid of the blood as so many micro- 

 gametes. If it comes into proximity with a macrogamete, the micro- 

 gamete dashes towards it, fuses with it (Fig. 23, K), and becomes drawn 

 in and completely merged with its substance. Complete nuclear fusion 



A B 



Fig. 24. 



Curve showing the fluctuation in body temperature in a person suffering from Malaria caused by 

 Plasmodium vivax. The temperature scale on the left is in degrees Centigrade, that on the right 

 in degrees Fahrenheit. The horizontal line indicates normal temperature. The vertical lines are 

 drawn at 24-hour intervals. Parasites {A, schizont ; E, group of merozoites) are drawn below the 

 curve to indicate the point about which schizogony takes place. 



takes place and there now exists a zygote in place of the two separate 

 gametes. 



The fact that these processes of maturation and syngamy are induced 

 by cooling the blood is correlated with the fact that this part of the life- 

 history takes place normally in the body of a cold-blooded insect — a 

 mosquito of the genus Anopheles or of one of -the genera allied to it. 

 When such a mosquito takes in a meal of malarial blood all the stages 

 of the parasite except the fully developed gametocytes are promptly 

 killed and digested. The gametocytes on the other hand give rise to 

 gametes in the way described, and zygotes are formed by the process 

 of syngamy. The zygote — the superficial layer of whose protoplasm 

 becomes modified to form a distinct thin membrane — soon loses its 

 spherical form, becoming somewhat pointed at each end, and becomes 

 an actively motile zygote or ookinete (Fig. 23, L). This creeps about 



