LIFE HISTORY 777 



Gametes cannot multiply in the blood of man and can only propagate their 

 species in the digestive tube of certain mosquitos. In the crescent forms of 

 gametes two kinds can be distinguished ; the female gametes or macrogametes 

 (fig. 374, E) which are longer, more slender and have the pigment more closely 

 concentrated about the nucleus, and the male gametes or microgametocytes 

 (fig. 374, D) which are shorter and stouter and have the pigment more scattered 

 through the cell protoplasm. 



[In the spherical forms of gametes the male and female cells are not so 

 easily distinguished though if the male cell be watched in a fresh preparation 

 under the microscope it will be seen in due course to extrude its flagella.] 



X- 1 X. 



I \ 



** 





G 





FIG. 374. The hsematozoon of malaria. Stained by Irishman's method. 

 Amoeboid or ring parasites : gametes : crescents : flagellated bodies. A, B, C, 

 amoeboid trophozoi'tes in a red cell ; D, male crescent ; E, female crescent ; 

 F, male spherical gamete ; G, macrogamete ; H, flagellated body or micro- 

 gametocyte ; I, fertilization of a macrogamete by a microgamete ; J, zygote. 



When a female mosquito of the genus Anopheles (the males do not bite) 

 bites a person suffering from malaria it withdraws a certain amount of blood 

 containing the various forms of the parasite which have already been 

 described : in the alimentary canal of the mosquito the young amoeboid 

 parasites and schizonts are rapidly destroyed but the gametes survive and 

 undergo sexual reproduction. The macrogametes, or female cells become 

 spherical and have a small irregular centrally situated mass of chromatin 

 (fig. 374, G). In the microgametocytes, or male cells, the chromatin splits, 

 generally into four secondary nuclei, (fig. 374, F) which travel towards the peri- 

 phery, protrude from the protoplasm of the cell and become drawn out into 

 long, slender, motile filaments, flagella or microgametes (fig. 374, H), which 

 soon become detached and go in search of the macrogametes. After the 

 flagella are detached the microgametocyte soon dies. The microgametes meet 

 the macrogametes in the stomach of the mosquito, penetrate and fertilize 

 them (fig. 374, I) : the fertilized macrogamete constitutes the zygote. 



The young zygote, spherical in the first instance, elongates (fig. 374, J), 

 moves towards the wall of the stomach of the mosquito and passes between the 



