TELOSPORIDIA 93 



red corpuscles, which then break up, setting free the schizozoites 

 (merozoites) and also products of the metaboUsm of the parasite which 

 cause fever. After some generations, gamonts similar to those of 

 Eimeria appear, but remain quiescent unless sucked up by a mosquito, 

 in whose gut the female gamont becomes a spherical macrogamete, the 

 male gamont throws off whip-like microgametes, and syngamy takes 

 place. The zygote becomes elongate and active (an ookinete), and 

 bores its way through the wall of the mosquito's stomach, on the 

 outside of which it becomes encysted (oocyst). Here its nucleus 

 divides and it breaks up into sporoblasts which in turn produce 

 spindle-shaped sporozoites. The oocyst now bursts, setting the sporo- 

 zoites free in the blood of the insect. They make their way into the 

 salivary glands and are injected with the saliva into a mammalian 

 host, where they give rise to trophozoites which infest the red 

 corpuscles. 



Three species of Plasmodium infest man — P. vivax which sets free 

 a generation of schizozoites in forty-eight hours, P. malariae which 

 does so in seventy-two hours, and P. falciparum whose schizogony 

 occurs at more irregular intervals. Since the attacks of fever take place 

 when the corpuscles break up and set free the toxins formed by the 

 parasites, the fever caused by P. vivax returns every third day and is 

 known as "tertian ague", and that caused by P. malariae ("quartan 

 ague") recurs every fourth day, while P. falciparum causes irregular 

 (quotidian) fevers which are more or less continuous. These latter 

 are the "pernicious malaria" of the tropics. The morphological 

 differences between the species are small, but P. vivax is distinguished 

 by the active movement of its pigment granules and the large number 

 (15-24) of its schizozoites, P. malariae by the sluggishness and often 

 quadrilateral form of its amoeboid stage, P. falciparum by the paucity 

 of its pigment and by its curved, sausage-shaped gamonts. 



Order GREGARINIDEA 



Telosporidia in which the adult trophozoite becomes extracellular; 

 and the female (as well as the male) gametes are merogametes. 



Intestinal and coelomic parasites of invertebrates, especially of 

 arthropods and annelids. 



Suborder SCHIZOGREGARINARIA 

 Gregarinidea which undergo schizogony. 



Schizocystis (Fig. 76). Parasitic in the intestine of the larvae of 

 dipterous flies. The young trophozoite attaches by one end to the gut 

 epithelium of the host. Its nuclei multiply. When ripe it undergoes 

 multiple fission. The products (schizozoites) either repeat asexual 



