Sexual Life Cycle 531 



paroxysms have occurred it may be observed that not all of 

 the schizonts change to meroblasts and form spores. Some 

 remain large spheroidal bodies or, as in Plasmodium falci- 

 parum, assume a peculiar crescentic form and remain un- 

 changed in the blood. These are the sexual parasites. The 

 female is usually the larger and is known as the makrogame- 

 tocyte, the male, the smaller, the micro gametocyte. These 

 are the bodies which when removed by the mosquito 

 lay the foundation of its infection. When they are with- 

 drawn for microscopic examination or exposed to the in- 

 testinal juices of the mosquito, the microgametocyte be- 

 comes tumultuous, its granules are observed to be in a state 

 of active cytoplasmic streaming, and suddenly there burst 

 forth long slender filaments, the micro gametes or sporozoits. 

 These correspond with the flagella of Laveran and others, 

 and are the same bodies that Manson thought might be 

 the form in which the parasite leaves the insect's body. 

 The microgametes lash vigorously for a time, then, breaking 

 loose, swim away, and, as MacCallum observed, conjugate 

 with macrogametes sexually perfect cells formed from the 

 macrogametocytes, thus fertilizing them. As the result of 

 this fertilization a zygote or ookinete is formed. It assumes 

 a somewhat elongate pointed form and attaches itself 

 to the wall of the mosquito's stomach. In the course 

 of time it penetrates and appears upon the outside, pro- 

 jecting into the body cavity. It grows larger and rounder, 

 divides into several segments, and eventually forms an 

 oocyst with many small cells, which break up into myriads 

 of tiny elongate fusiform bodies, the sporozoits. These, 

 in the course of time, seem to find their way to the sali- 



to i2b, microgametocytes still in the circulatory blood of man. If the 

 macrogametocytes (i2a) are not taken into the alimentary canal of the 

 mosquito, they multiply parthenogenetically (i2a, I3C to lye) and the 

 resulting merozoits (lye) become schizonts (3 to 7). The figures below 

 the dotted line represent what takes place in the alimentary canal of 

 anopheles (13 to 17); i3b and i^b the formation of microgametocytes; 

 i3a and i3b, maturation of the macrogametes; isb, a microgamete;i 6, 

 fertilization; 17, ookinete; 18, ookinete on the wall of the mosquito's 

 stomach; 19, penetration of the gastric epithelium by the ookinetes; 20 

 to 25, stages of sporogenesis on the outer wall of the mosquito's stomach; 

 26, migration of the sporozoits to the salivary glands of the mosquito; 27, 

 salivary gland with sporozoits in the epithelial cells, and escape of the 

 sporozoits from the salivary glands through the insect's proboscis at 

 the time a human host is bitten; i, free sporozoit from the mosquito's 

 saliva in the human blood; 2, penetration of the sporozoit into a red 

 blood-corpuscle, beginning the human cycle again (Liihe). 



