l62 THE ANIMAL PARASITES OF MAN 



relatively healthy periods the number of parasites in the blood falls 

 below that necessary to provoke febrile symptoms ; relapses then 

 result merely from increase in the numbers of the parasites present in 

 the individual. Ross's view is now generally accepted. 



If the gametocytes, which are globular, or in the pernicious 

 or malignant tertian parasite crescentic (fig. 81), gain access to the 



(1 <^^f 



N* y^ V - 



FIG. 81. Stages of development of pernicious or malignant tertian parasites in the intestine 

 of Anopheles maculipennis. (After Grassi.) a, macrogametocyte (crescent) still attached to 

 human blood corpuscles; b, macrogametocyte (sphere) half an hour after ingestion by the 

 mosquito ; c, microgametocyte (crescent) attached to the blood corpuscle ; d, microgameto- 

 cyte (sphere) half an hour after ingestion ; the nucleus has divided several times ; e, micro- 

 gametes attached to the residual body (polymitus stage). 



intestine of an Anopheline, 1 they mature. The macrogametocytes 

 extrude a part of their nuclear substance (fig. 80, ija, iqa] and 

 thereby become females or macrogametes. The microgametocytes, on 

 the other hand, undergo repeated nuclear division, preparation for 

 this being made apparently whilst in the blood of man. This results 









FIG. 82. Ookinete of the malignant tertian parasite in the stomach of Anopheles maculipennis, 

 thirty-two hours after ingestion of blood. (After Grassi.) 



in the formation of threadlike bodies which move like flagella and 

 finally detach themselves from the residual body (fig. 80, 736, 746). 

 These are the males or microgametes 2 (fig. 80, 756). 



Copulation takes place in the stomach of the Anopheline (fig. 80, 16). 

 A microgamete penetrates a macrogamete and coalesces with it. The 



1 Schizonts ingested about the same time perish in the intestine of the mosquito. 



2 If the microgametocytes are sufficiently mature the formation of microgametes occurs in 

 the blood of man as soon as it is taken from the blood-vessel and has been cooled and 

 diluted. Such a stage is called a Polymitus form, and the process has been called 

 " exflagellation." 



