ANIMAL PARASITES 



85 



mosquitoes on successive days. In such cases parasites in various 

 stages will be found on the one slide. 



The parasite is injected into the blood of man by the bite of 

 an Anopheles mosquito, in the form of an elongate veriform 

 sporozoite. This stage will not be found in blood smears. The 



Schizogony 



in blood of 



man 



Sexual feneration 

 and 

 Sporooony 

 in the 

 mosquito 



Fig. 27. — Diagram of the life cycle of a malarial parasite. The upper figures 

 illustrate the asexual cycle of Plasmodium virax in human blood ; to the right are 

 the sexual forms of P. falciparum in the stomach of the mosquito and to the left 

 are the stages to be found in the stomach wall and salivary glands of the insect 

 host. {After Minchin.) 



youngest stage to be noted is the signet ring stage, so called 

 because the protoplasm consists of a ring staining blue, with a 

 clear unstained space, and a red-staining spot, the nucleus, 

 suggesting the seal of a ring. This growing stage is called, as in 

 other Sporozoa, the trophozoite. 



As the parasite grows, the ring of protoplasm enlarges and a 

 dark brown pigment, derived from the haemoglobin of the blood 



