358 THE PROTOZOA 



vided the word be not written in italics or with an initial capital 

 letter ; anything is better than to speak of them as " plasmodia." 



In human beings three distinct species at least of hsemamcebse 

 are recognized namely, the parasites of tertian, quartan, and 

 pernicious or tropical malaria, now generally named Plasmodium 

 vivax, P. malarice, and P. falciparum, respectively ; the last-named 

 is distinguished from the other two by the sporonts being crescent- 

 shaped, and was put formerly in a distinct genus, Laverania, which 

 has been abolished . Hsemamcebse similar to those causing malaria 

 in man have been described from other mammals for example, 

 monkeys, several species ; bats ; and squirrels. The human 

 malarial parasites go through their sporogony in mosquitoes of the 

 subfamily Anophelinse ; the life-cycle of those of other mammals 

 has not been yet fully investigated. 



In birds hsemamcebse are of very common occurrence. For 

 these Labbe created the genus Proteosoma, a name still in use 

 unofficially as a distinctive appellation ; but the correct name of 

 the avian malarial parasites, commonly assumed to belong all to 

 one species, is variously stated to be Plasmodium prcecox or P. re- 

 lictum. In contrast with the human malarial parasites, those of 

 birds are transmitted by mosquitoes of the subfamily Culicinse. 



Lastly, parasites are known, from certain reptiles, which are 

 intracorpuscular in habitat, amoeboid in form, and produce pig- 

 ment. Hence they appear to be genuine hsemamcebae, but they 

 do not exflagellate when the blood is drawn,* and very little is 

 known of their life-cycle. By some authorities these reptilian 

 forms are referred also to the genus Plasmodium, but it is best 

 for the present to maintain the genus Hcemocystidium, Castel- 

 lani and Willey, for these reptilian forms. Examples are H. metsch- 

 nikovi (Simond), from an Indian tortoise, Trionyx indicus ; H. 

 simondi, Castellani and Willey, from a Ceylon gecko, Hemidactylus 

 leschenaulti ; and various other species. 



Since the transmission of the malarial parasites by mosquitoes 

 was first discovered by Ross in his experiments on the Proteosoma- 

 parasite of birds, the development of human malarial parasites 

 has been studied in full detail by numerous investigators, amongst 

 whom Grassi and Schaudinn (130) must be specially mentioned. 

 Consequently the life-cycle of these parasites is better known than 

 that of almost any other Protozoa, and is now to be found described 

 in every textbook. It will be sufficient, therefore, to describe the 

 life-cycle of the species parasitic in human beings in brief outline, 

 as typical of this class of parasites (Fig. 156). 



* Aragao and Neiva have observed in Plasmodium (Hcemocystidium) diploglos.si 

 that, in the male gametocytes on the slide, violent streaming movements occur, 

 such as are the prelude, in other haemamcebaa, to exflagellation ; but formation of 

 gametes was not seen. 



