THE SPOROZOA 243 



The majority of experts, however, are agreed in recognising three 

 distinct species, divided amongst two different genera. 1 These 

 are (1) Laverania malariae, Gr. et Fel., the parasite of pernicious 

 malaria; (2) Plasmodium malariae (Lav.), the parasite of quartan 

 ague ; and (3) Plasmodium vivax (Gr. et Fel.), the parasite of 

 tertian ague. The following account refers more especially to 

 the first of these, but the peculiarities which characterise the 

 other two will be briefly mentioned by way of comparison. 2 



The minute sporozoites, introduced into the human blood by 

 the bite of a mosquito, attack and penetrate red blood-corpuscles, 

 probably in a way similar to the infection of epithelial cells by 

 Coccidian parasites.' Each sporozoite (" exotospore," Lankester) 3 

 is slender, almost filamentous in form, the body sharply pointed 

 at each end, with a thicker central portion in which the nucleus is 

 lodged (Fig. 68, XIX). Within the blood-corpuscle the sporozoite 

 rounds itself off and develops into an amoeboid trophozoite, which 

 grows at the expense of the blood-corpuscle until it nearly fills 

 it (Fig. 68, I-V). The youngest amoebulae are without any pig- 

 ment, but usually contain, in fixed and stained preparations, 

 a conspicuous vacuole, giving the parasite the so-called ring-form. 

 With further growth the vacuole disappears, and grains of pig- 

 ment termed melanin, representing, probably, an excretory product, 

 are formed in the body of the parasite and collect towards the 

 centre near the nucleus. When full-grown the trophozoite acquires 

 a rounded form and is now a ripe schizont (" sporulating body," 

 " sporocyte "), ready to reproduce itself by schizogony (Fig. 68, 

 6). The nucleus divides to form a variable number of daughter 

 nuclei, which travel to the periphery (Fig. 68, 7, 8). The proto- 

 plasmic body becomes divided up into a corresponding number of 

 segments, the merozoites (" enhaemospores," Lankester), centred 

 round a small mass of residuary protoplasm, in which all . the pig- 

 ment-granules are deposited (Fig. 68, 9). This characteristic form 

 of the parasite, known as the rosette-stage (" corps en rosace "), 

 corresponds to the so-called "Eimerian cysts" of the Coccidia. 

 When the schizogony is complete, or, it may be, during the initial 

 stages of this process, the exhausted blood-corpuscle breaks up, 



1 See also footnote to p. 267. 



2 Since the account here given of the life-cycle of the malarial parasites was 

 written, the very important monograph of Schaudinn [94a] upon the tertian parasite 

 has come to hand, just as the proofs of this article are going to be paged. It is there- 

 fore, unfortunately, not possible to introduce any of Schaudinn's figures ; but had his 

 memoir appeared earlier, some portions of Fig. 68 might have been made less 

 diagrammatic. 



3 Numerous terminologies have been suggested, and are in use, for the phases of 

 the malarial parasite ; the most recent is that suggested by Lankester, in Nature, vol. 

 Ixv. No. 1691 (27th March 1902). The scientific terminology of Schaudinn, already 

 introduced above for the Coccidia, is employed here, but reference is also made to 

 other names applicable specially to the various stages of the malarial parasites. 



