(1) The _Plasmodium_ or _Hæmamœba_ type. This includes the malarial parasites of man and of birds. The asexual multiplicative or schizogonic phases occur inside red blood corpuscles and are amœboid. They produce distinctive, darkish pigment termed melanin or hæmozoin. Infected blood drawn and cooled on a slide may exhibit “exflagellation” of the male gametocytes, _i.e._, the formation of filamentous male gametes. The invertebrate host is a mosquito. The malarial parasites of man are discussed at length on p. 155. Similar pigmented hæmamœboid parasites have been described in antelopes, dogs, and other mammals, and even reptiles. (2) The _Halteridium_ type. The trophozoite stage inside the red blood corpuscle is halter-shaped. Pigment is produced, especially near the ends of the organism. The parasites occur in the blood of birds. The invertebrate host of _H. columbæ_ of pigeons in Europe, Africa, Brazil and India, is a hippoboscid fly, belonging to the genus _Lynchia_. Halteridium parasites are common in the blood of passerine birds, such as pigeons, finches, stone owls, Java sparrows, parrots, etc. The Halteridium embraces or grows around the nucleus of the host red cell without displacing the nucleus. Young forms and multiplicative stages of _H. columbæ_ have been found in leucocytes in the lungs of the pigeon (fig. 76, _8_-_12_). Male and female forms (gametocytes) are seen in the blood (fig. 76, _3a_, _3b_). The cytoplasm of the male gametocytes is pale-staining and the nucleus is elongate, while the cytoplasm of the females is darker and the nucleus is smaller and round. Formation of male gametes from male gametocytes (the so-called process of “exflagellation”) may occur on a slide of drawn infected blood, also fertilization, and formation of the oökinete, as first seen by MacCallum. The correct generic name for Halteridia is, apparently, _Hæmoproteus_. Wasielewski (1913), working on _H. danilewskyi_ (var. _falconis_), in kestrels, finds that the halteridium may be pathogenic to nestlings. The cycle of _H. noctuæ_ described by Schaudinn (1904) lacks confirmation. The account of the life-cycle of _H. columbæ_ given by Aragão (1908) is illustrated in fig. 76. It agrees with the work of Sergent (1906–7) and Gonder (1915). Mrs. Adie (1915) states that the cycle in _Lynchia_ is like that of a _Plasmodium_. [Illustration: FIG. 76--_Hæmoproteus_ (_Halteridium_) _columbæ_. Life-cycle diagram: 1, 2, stages in red blood corpuscle of bird; 3, 4, gametocytes (3_a_ ♂, 3b ♀); 5_a_, formation of microgametes; 6, fertilization (in fly’s gut); 7, oökinete; 8–12, stages in mononuclear leucocytes in lungs. (After Aragão.)]