MALARIA PARASITES 



73 



<ES 



ment. They remain in the corpuscle where they arose from a 

 merozoite, and undergo no change unless they be sucked in by a 

 gnat ; but in that case, whereas all other forms of the parasite 

 die and are digested by the gnat, the gamonts, becoming free 

 by the breaking up of their corpuscles, proceed to develop 

 gametes. They are of two kinds, male and female, the former with 

 a larger nucleus and more lightly staining cytoplasm than the 

 latter. In the male gamont the nucleus breaks rapidly into some 

 half-dozen fragments, leaving a residual mass in the central 

 cytoplasm. The daughter nuclei come to the surface, and grow 

 out, with a suddenness which is almost explosive, into fine threads 

 of nucleoplasm, projecting from 

 the body in scarcely perceptible 

 sheaths of cytoplasm. These are 

 the microgametes. They lash 

 violently, dragging about the 

 residue of the gamont body, till 

 they break free. The remains of 

 the gamont perish. The female 

 gamont, by a process in which 

 the nucleus loses a part of its 

 contents, becomes a single macro- 

 gamete. It is now ripe for fertilisa- 

 tion by a microgamete which 

 penetrates the body, and the nuclei 



(male and female pronuclei) fuse. The zygote changes from a 

 rounded to a worm-Hke creature called an ookinete, which glides 

 about by contractions of its body, pierces the epithelium of the 

 insect's stomach with one end, which is pointed for the purpose, 

 and comes to rest in the sub-epitheHal tissue, where it rounds 

 itself off and forms a structure called an oocyst. It is also known as 

 the sporont on account of its further history, which is as follows. 

 Through its thin cyst-wall the parasite continues to absorb 

 nutriment, and grows in size, bulging out the wall of the stomach 

 into the body cavity so as to form a kind of blister (Fig. 44). 

 As it grows, its nucleus multiphes by binary fission and cytoplasm 

 becomes concentrated round each nucleus to form a body known 

 as a sporoblast. Now the nucleus of each sporoblast divides 

 repeatedly and the surface of the body grows out into slender 

 processes, into each of which one of the daughter nuclei passes. 

 Finally the processes break off, and so the cyst contains hundreds 



Fig. 44. — Part of the alimentary 

 canal of a mosquito infested with 

 Plasmodium. — From Lankester's 

 Zoology, after Ross. 



cy., Cysts of the parasite ; int., intestine; 

 M.t., Malpighian tubes; ces., oesophagus; 

 St., stomach. 



