444 BIOLOGY OF THE PROTOZOA 



Family 2. Plasmodidse, the malaria organisms. These are blood para- 

 sites of birds and man causing malarial fevers. Agametes are formed in 

 the red blood cells as are also the gametocytes. The latter mature in the 

 stomach of the mosquito (species of Culex and Anopheles), zygotes are 

 formed wWch penetrate the wall of the stomach and form sporocysts 

 against the subepithehal tissue. Here, within a delicate membrane, the 

 sporozoites are formed in groups resembling sporoblasts. The sporozoites, 

 liberated into the body cavity of the mosquito, are transmitted with fluids 

 from the salivary gland to the blood stream of the vertebrate host. Blood 

 parasites of bats and of reptiles are also included here. All have the com- 

 mon property of forming pigment (melanin) at the expense of the haemo- 

 globin. 



2. Genus Proteosoma, Labb6 (1894). The cause of bird malaria, trans- 



mitted by different species of the mosquito family Culicidse. Widely 

 distributed as bird parasites throughout the world. Probably 

 several species but not easily distinguished from the best known 

 form Proteosoma prcecox of Grassi and Feletti (1890). 



3. Genus Plasmodium, Marchiafava and Celli (1885). The human mala- 



ria organisms best knowai by the common names of tertian fever 

 parasites causing pyrexial attacks every third day, c^uartan parasites 

 causing attacks every fourth day, and tropical fever parasites 

 causing attacks daily or irregularly. Transmission by mosquitoes 

 of the family Anophelida?. Characteristics of the family. Differ- 

 ent species are recognized according to the clinical history or by 

 differences in the gametocytes. Thus P. vivax, Grassi and Feletti 

 (1892), is the cause of tertian fever, P. malarice Laveran (1883), the 

 cause of quartan fever and P. falciparum, Welch (1897), the cause 

 of tropical fever. In the last species the gametocytes are large 

 and crescentic and differ from the gametocytes of other species and 

 for this reason together with the clinical differences, the species is 

 regarded by some authorites as having generic value and has been 

 named by Grassi and Feletti Laverania malarice in honor of the 

 original discoverer. 



In addition to man and birds other types of mammals are subject 

 to blood infection by species of Plasmodium. Monkeys in partic- 

 ular are subject to infection, so also are bats (Dionisi) and squirrels. 



4. Genus Achromaticus, Dionisi (1898). Questionably included here 



until the life history is known. The sporozoites form rings in the 

 red blood corpuscles of the bat (Fesperu^o species) and give rise to 

 four agametes, pyriform cells resembling Babesia (see below) . Pri- 

 mary host unknown although Neumann believes he has found devel- 

 opmental stages in the bat louse Pteroptus vespertilionis. It differs 

 from other Plasmodidse in the absence of pigment. 



5. Genus Hcemocystidium, Castellani and Willey (1904). Blood parasites 



of reptiles with pigment formation. Agametes two or sometimes 

 four in number are formed in the peripheral blood, gamogony 

 unknown, primary host unknown, included here provisionally (see 

 Shortt, 1922). 



Family 3. Babesiidae. These are unpigmented parasites of small size 

 found in the blood corpuscles of various mammals and transmitted by ticks. 

 Amoeboid, circular and ring form, and pyriform stages have been described 

 for the same organism. Agamogony by binary division, budding, or mul- 

 tiple division. There is little actual knowledge of the sexual phases in the 

 tick, if they exist, but there is much speculation regarding them. Many 

 genera have been described but until the life history is fully known it seems 

 better to regard them as sub-genera of the original genus Babesia of Star- 

 covici, 1893. 



