THE H^MOSPORIDIA 357 



In the sequel, therefore, the Hsemosporidia will be discussed 

 under five principal types, each of which comprises several forms. 

 So far as possible, the " correct " names of these forms will be 

 stated. Finally an attempt will be made to discuss the position 

 and affinities of the group as a whole. The following is a summary 

 of the distinctive characters of the types in question : 



1. The Hcemamoeba-Type. The trophozoites of the schizogonous 

 cycle occur within red blood-corpuscles, and are amoeboid ; they 

 produce a characteristic pigment, termed " melanin." When the 

 blood is drawn and cooled down on a slide, the male sporonts, if 

 present, form filamentous male gametes resembling flagella, and 

 are consequently said to " exflagellate." The invertebrate host, 

 so far as is known, is a mosquito. 



2. The'Halteridium-Type. The intracorpuscular trophozoite is a 

 characteristic halter-shaped parasite of red blood-corpuscles', which 

 is amoeboid, and which, like the last, produces melanin-pigment, 

 and " exflagellates " on the slide. Only known from the blood of 

 birds ; the invertebrate host, so far as is known, is a Hippoboscid fly. 



3. The Leucocytozoon-Type. The full-grown sporonts are found 

 within white blood-cells, which are greatly altered by the parasite. 

 They are not amoeboid, and do not produce pigment, but they 

 " exflagellate " when the blood is drawn. Only known in birds ; 

 the invertebrate host is unknown. 



4. The Hcemogregarine-Type. Parasites usually of red blood-cor- 

 puscles, sometimes of white ; they are not amoeboid, do not produce 

 pigment, and do not " exflagellate." They occur throughout the 

 whole vertebrate series, but are most abundant in cold-blooded 

 vertebrates. Those of fishes, amphibia, and reptiles, are trans- 

 mitted generally by leeches ; those of mammals and some reptiles 

 apparently by ectoparasitic Arthropods. 



5. The Piroplasma -Type. Parasites of red blood - corpuscles, 

 amoeboid or of definite form ; they do not produce pigment and 

 do not "exflagellate"; generally very minute. They are known 

 only in mammals, and the invertebrate host is always a tick. 



These five types will now be considered in more detail. 



1. The Hcemamcebce. The characteristic form of parasite in this 

 section is a minute, amoeba-like organism contained within a red 

 blood-corpuscle ; as it grows it gradually exhausts and destroys the 

 corpuscle, and at the same time produces the characteristic melanin- 

 pigment. Such are the well-known malarial parasites of mammals 

 and birds. Unfortunately, the accepted rules of nomenclature 

 render it obligatory to use the generic name Plasmodium for these 

 parasites, a most unsuitable name, since they are not plasmodia 

 in any phase except very temporarily, when they are sporulating. 

 They may, however, be termed familiarly " hsemamcebae," pro- 



