364 THE PROTOZOA 



and form masses of pigment, the so-called " black spores " of Ross. Similar 

 degeneration-phenomena have been observed by Schauclinn (147) in the 

 oocysts of Cyclospora caryolytica, and may be compared to the transformation 

 of chromidia into pigment in the degeneration of Actinosphcerium in cultures 

 (p. 209). 



The " exflagellation," or formation of microgametes, which takes place, 

 under normal circumstances, in the stomach of the mosquito, can be seen also 

 in blood freshly drawn and examined on a slide, if ripe sporonts are present. 

 The process is greatly furthered by lowering the density of the blood for 

 example, by adding to it not more than one- fifth of its volume of ordinary 

 water, or by simply breathing on the blood when drawn (compare Neumann, 

 77). 



It is curious that, while so many experimenters have established absolutely 

 beyond all doubt the transmission of hsemamcebse by mosquitoes, those of man 

 by anophelines, and those of birds by culicines, no experiments seem to have 

 been performed to determine how long a mosquito, once infected, remains 

 infective without being reinfected. In other cases of similar transmission, 

 such as that of trypanosomes, yellow fever, etc., it is known that the inverte- 

 brate host, once rendered infective, remains so for a very long time, probably 

 for the rest of its life. In the case of malarial parasites this point remains to 

 be tested experimentally. 



The haemamcebse of Primates have been studied by a number of investigators, 

 and several species distinguished : Plasmodium kochi (Laveran) from the chim- 

 panzee and various African monkeys ; P. pithed from the orang-outang, and 

 P. inui from Macacus spp. (Halberstaedter and Prowazek, Mathis and Leger, 

 473) ; P. cynomolgi from Macacus cynomolgus (Mayer, A.P.K., xii., p. 314) ; 

 and P. brasilianum from the ouakari, Brachyurus calvus (Berenberg-Gossler). 

 The schizogony appears to be generally similar to that of the species parasitic 

 in man ; ring-stages occur, and the multiplication is in some cases similar 

 to the tertian, in other cases to the quartan parasite. Binucleate trophozoites 

 are of common occurrence, and binary fission also occurs (Flu, A.P.K., xii., 

 p. 323). A striking feature of monkey- malaria is the comparative rarity 

 of multiplicative phases, which may be in relation to the fact that these 

 parasites cause no appreciable symptoms of disease in their hosts ; in both 

 respects they are comparable to non-pathogenic trypanosomes. Transmission 

 is probably effected by anopheline mosquitoes (Mayer). 



In bats two distinct forms of intracorpuscular parasites have been described 

 under distinct generic names : PolycJiromophihis, from Vespertilio and Miniop- 

 terus spp., and Achromaticus, from Vesperugo spp. These two genera are 

 distinguished by the fact that Polychromophilus produces melanin -pigment, 

 and Achromaticus does not. Polychromophilus is apparently an ordinary 

 haemamceba which should be included in the genus Plasmodium. Achro- 

 maticus, on the other hand, appears, from the recent investigation of Yakimoff 

 and others (753), to be a true piroplasm (see below). 



Plasmodium vassali from squirrels has ring-like young trophozoites, and 

 its schizogony takes place by binary or multiple fission, more commonly the 

 former (Vassal) ; some forms of the parasite figured resemble Piroplasma. 



The life-history of the Proteosoma- parasite of birds has been studied in 

 detail by Neumann ; the principal phases of the parasite are essentially similar 

 to those of the hsemamcebse parasitic in man. Experimenting with canaries, 

 Neumann transmitted the infection by means of Stegomyia fasciata, but this 

 mosquito was found to be less efficient as a host for Proteosoma than the 

 species of Culep. Of Stegomyia only 11 '4 per cent, developed ripe cysts, as 

 against 85 per cent, of Culex ; the development of the parasite is accomplished 

 in nine to eleven days in Culex, in thirteen to fifteen days in Stegomyia ; and 

 a far smaller number of the parasites succeed in developing in Stegomyia, in 

 which the maximum number of cysts seen in the stomach of any mosquito 

 was thirty-six, while in Culex much larger numbers, 500 to 1,000, are recorded. 



But little is known of the life-cycle of the reptilian hsemamcebse of the 

 genus Hcemocystidium. Aragao and Neiva have described schizogony of the 



