Chapter V 
The Malarial Parasite 
Life History 
The Protozoa are divided into several classes, one 
of which is the Sporozoa. 
This class comprises several orders, the most closely 
allied of which are the Gregarinida (e.g., Monocystis 
agilis in the seminal vesicles of the earth worm), the 
Coccidiidea ( e.g ., Coccidium oviforme in the rabbit’s 
liver) and the Haemosporidia (which include the 
malarial parasites of man, birds, etc.). There is a close 
relationship between the Coccidiidea and the Haemos¬ 
poridia (malaria parasites), the developmental cycles 
of the two being almost identical. The develop¬ 
mental cycle in the blood (the febrile cycle) of the 
malaria parasites was first demonstrated by Golgi, the 
further cycle in the mosquito by Ross. The cycle 
of Golgi is the asexual cycle, producing auto-infection 
of the patient ; the cycle of Ross is the sexual cycle, 
producing a new infection in a healthy subject. 
The sexual cycle, it has been thought, commences 
in the blood when the conditions are unfavourable 
for the continuance of the asexual cycle, and, in fact, 
has been taken as a sign that the patient has already 
developed immunity against the fever-producing 
young parasites (spores). Thus it is well known that 
in malignant tertian the sexual forms, gametes or 
crescents, first appear about a week to ten days after 
