352 



EVOLUTION AND ANIMAL LIFE 



brutes as intermediate or alternate hosts). Certain kinds are 

 found in the cold blood of fishes, amphibians, reptiles, and 

 certain others in the warm blood of birds and mammals. The 

 genera H alter idium and Plasmodium contain certain species 

 that live exclusively in the blood of birds or mammals for part 

 of their life and in the bodies of certain arthropods for the 

 other part of their life. They produce a series of asexual 

 generations (reproduction by simple division or sporulation) 

 in their vertebrate hosts, and a sexual generation (reproduction 



by the development 

 of a zygote formed 

 by the fusion of two 

 cells, called gametes) 

 in the arthropod host. 

 This arthropod host 

 for all the species so 

 far known of these 

 genera is exclusively 

 the mosquito. Three 

 species of the genus 

 Plasmodium, namely, 

 P. vivax, P. malarice, 

 and P. falciparum, are 

 the specific causal 

 agents of the distinct 

 malarial fevers know r n 

 as tertian, quartan, 

 and tropical fever re- 

 spectively. (In the 



literature of "mosquitoes and malaria/' the name " Hcema- 

 moeba' will be found to be used synonymously with Plas- 

 modium.) 



Laveran, a French surgeon in Algiers, discovered the Plas- 

 modium parasite in the red blood corpuscles of malarial fever 

 patients in 1880, and determined that the disease was actually 

 and solely due to the destructive and toxic effects of the growth 

 and multiplication of the parasite in the blood. Every forty- 

 eight hours in tertian fever (seventy-two hours in quartan) there 

 is completed a whole (asexual) cycle in the life of one of these 

 parasites, including its birth by the division of the body of 

 the mother into several small merozoites, the penetration of 



FIG. 211. The life cycle of Coccidium lithobii, Proto- 

 zoan parasite of the centipede, Lithobius. (After 

 Schaudin.) 



