These genera belong to the suborder 

 Haemospororina, which is differentiated 

 from the Eimeriorina and Adeleorina by 

 the facts that the microgametocyte pro- 

 duces a moderate number of microgametes 

 and the sporozoites are naked. The gam- 

 onts are similar and develop independently. 

 The zygote is motile (i.e. , it is an ookinete). 

 All species are heteroxenous; schizogony 

 takes place in a vertebrate host, and spor- 

 ogony in an invertebrate. If the erythro- 

 cytes are invaded, pigment (hemozoin) is 

 formed from the host cell hemoglobin. 



This suborder was customarily div- 

 ided into 2 families, the Plasmodiidae 

 containing the genus Plasmodium, and the 

 Haemoproteidae containing the genera 

 Haenioprotens and Leiicocytozoon. The 

 principal difference was that in the Plas- 

 modiidae schizogony was thought to take 

 place only in the erythrocytes, while in 

 the Haemoproteidae it takes place in the 

 lungs, liver, spleen, kidneys and other 

 internal organs. However, when the com- 

 plete life cycles of several species of 

 avian and human Plas)}io(lium were worked 

 out (Huff and Coulston, 1944, 1946; Shortt 

 and Garnham, 1948; Short et al. , 1951; 

 Garnham, 1954; Bray, 1957), it was real- 

 ized that schizogony may occur both within 

 the erythrocytes and exoerythrocytically. 

 The distinction between the two families 

 is thus an artificial one, and there is no 

 point in retaining more than a single fam- 

 ily in the suborder. 



It is likely, as Manwell (1955) has 

 suggested, that the Haemospororina may 

 well have arisen from the coccidia of ver- 

 tebrates rather than from those of insects, 

 as had been more commonly supposed. 

 Genera like Lankesterella and Schellackla, 

 in which schizogony, gametogony and 

 sporogony all take place in the vertebrate 

 host and in which the sporozoites invade 

 the blood cells and are transmitted by 

 mites or other blood-suckers, could well 

 be the starting-point for the transition 

 from the Eimeriorina to the Haemospor- 

 orina. 



'■4^^ MAiS, 



KY ]^| 



Chapter 10 



PLASMODIUM 

 HAEMOPROTEUS 



AND 

 LEUCOCYTOZOON 



- 259 



