This type of Haemosporidia is characterized by invasion of red cells, amoeboid movement, pigment production and the extrusion of flagellum-like processes from the male sporont after the blood is taken from the animal and allowed to cool. Other Haemosporidia which are very important in diseases of domesticated animals, but not for man, are those of the piroplasm type. These parasites of the red cells do not produce pigment and do not “exflagellate.” It is to parasites of this type that some authorities have ascribed the cause of blackwater fever, a condition undoubtedly connected with malaria. It has been thought proper by some to consider the malarial parasites as belonging to two genera, the genus _Plasmodium_, characterized by round sexual forms and including _P. vivax_ and _P. malariae_ and the genus _Laverania_, characterized by crescent-shaped sexual forms and including but one species _L. malariae_, that of aestivo-autumnal malaria. Craig recognizes a quotidian form and a tertian form for the aestivo-autumnal parasite. Manson formerly held the view that three different species of crescent-bearing parasites were concerned in malignant infections; one, of tertian periodicity, _Laverania malariae_, and two, of quotidian periodicity, _L. praecox_, a pigmented form, and _L. immaculata_, a form in which pigment is only observed in the crescent formation and does not exist in the ring form schizonts. He has abandoned this view. Stephens has noted a parasite which has more nuclear material than _P. falciparum_ (_P. tenue_). _Malaria of Animals_.—Other Haemosporidia of the haemamoeba type are found in birds, monkeys, bats, squirrels and possibly in reptiles (the parasites of reptiles, while intracorpuscular and pigment producing, do not exflagellate). Of particular interest is the so-called bird malaria or _Proteosoma_, a parasite very similar to the human malarial ones. The life cycle of this parasite was demonstrated before that of the malarial parasites of man. Although Koch in his work showed that these malaria-like parasites of other animals were not infectious for man, Fermi has recently carried out well-controlled experiments, by feeding laboratory bred anophelines on the blood of various animals showing such infections, and subsequently on men, with invariably negative results. Accumulated experience shows that man is not susceptible to any of the animal malarias and that the three human species can only exist in man as an intermediate host and in certain species of anopheline mosquitoes as definitive hosts. Culicine mosquitoes never transmit malaria.