154 MALARIA 



crescents (Fig. 43 K and L). Just as in the case of other kinds 

 of animals and plants, nature has adapted these animals to cope 

 with their environment. As long as the blood of their host forms 

 a suitable environment they continue to multiply in the normal 

 manner, but when conditions due to the formation of antibodies 

 become unfavorable they produce these sexual crescents in large 

 numbers and patiently await rescue at the hands, or rather the 

 beak, of a mosquito. The crescents may persist in the blood for 

 several weeks, gradually disappearing after all other symptoms 

 of infection have vanished. Only slight differences can be seen 

 between the male and female gametocytes, the female being more 

 granular in appearance, and with the pigment particles arranged 

 in a more regular triangular manner (Fig. 43K and L). 



Mosquito Cycle. — When sucked into the digestive tract of the 

 mosquito these gametocytes begin a complex developmental 

 cycle, providing conditions of temperature are favorable. The 

 77iust favorable temperatures are between 75° and 85° F. The 

 digestive fluids dissolve the remnant of the blood corpuscles, but 

 the crescents resist digestion (Fig. 43M and N) and become more 

 obviously sexually differentiated. The male gametocyte de- 

 velops into a " flagellated body " (Fig. 43P), a little sphere from 

 which several long slender filaments project. These are very 

 active, constantly lashing to and fro, and ultimately break loose 

 and wriggle about in the stomach of the mosquito like little 

 spermatozoa, which, in effect, the}^ are. The female gameto- 

 cyte develops into an inactive sphere or gamete (Fig. 430) and 

 one of the filaments from the flagellated male enters to fertilize 

 it (Fig. 43Q). How perfectly the process simulates the act of 

 fertilization of an egg by a spermatozoan in the higher animals! 



The result of the union of the filament from the flagellated 

 body with the inactive female gamete is a body which corre- 

 sponds in every way to a fertilized egg of a higher animal. This 

 new individual, the beginning of a new generation, grows, elon- 

 gates, and becomes quite like a little worm (Fig. 43R). It now 

 wriggles and worms itself about in the stomach of the mosquito 

 and penetrates the wall, lodging itself between the inner and 

 outer linings of the stomach (Fig. 43S). Here more rapid growth 

 takes place and a heavy capsule develops, protruding on the outer 

 surface of the mosquito's stomach like a wart (Fig. 45). Mean- 

 while the contents of the capsule undergo important changes, 



