The hæmogregarines occurring in the white cells (mononuclears or polymorphonuclears) of mammals have been referred to a separate genus, _Leucocytogregarina_ (Porter) or _Hepatozoön_ (Miller). Such leucocytogregarines are known in the dog (fig. 79), rat, mouse, palm-squirrel, rabbit, cat, etc. Schizogony of these forms occurs in the internal organs, such as the liver, lung and bone-marrow of the hosts. They are apparently transmitted by ectoparasitic arthropods, such as ticks, mites, and lice. [Illustration: FIG. 78.--Hæmogregarines from lizards, _a_, _H. schaudinni_, var. _africana_, from _Lacerta ocellata_; _b_, _H. nobrei_ from _Lacerta muralis_; _c_, _H. marceaui_ in cytocyst, from _Lacerta muralis_. (After França.)] A few hæmogregarines are known to be parasitic in the red blood corpuscles of mammals. Such are _H. gerbilli_ in the Indian field rat, _Gerbillus indicus_; _H. balfouri_ (_jaculi_) in the jerboa, _Jaculus jaculus_, and a few species briefly described from marsupials. These parasites do not form pigment. Strict leucocytic gregarines have been described from a few birds by Aragão and by Todd. The sporogony of hæmogregarines is only known in a few cases, and in those affinity with the Coccidia is exhibited. In fact, the Hæmogregarines are now classified by some authors with the Coccidia. (5) The _Babesia_ or _Piroplasma_ type. These are small parasites of red blood corpuscles of mammals. They do not produce pigment. They are pear-shaped, round or amœboid in Babesia, bacilliform and oval in other forms referred to this group. Piroplasms are transmitted by ticks. These parasites are described at length on p. 172. [Illustration: FIG. 79.--_Leucocytogregarina canis_. Life-cycle diagram. Constructed from drawings by Christophers. (After Castellani and Chalmers.) Schizogony occurs in the bone-marrow. The parasite is transmitted from dog to dog by the tick, _Rhipicephalus sanguineus_, development in which, so far as known, is shown on the right.] THE MALARIAL PARASITES OF MAN. Malaria, otherwise known as febris intermittens, chill-fever, ague, marsh fever, paludism, etc., is the name given to a disease of man, which begins with fever. It has been known since ancient times and is distributed over almost all the world, although very unevenly, but does not occur in waterless deserts and the Polar regions. In many places, especially in the civilized countries of Central Europe, the disease is extinct or occurs only sporadically, and large tracts of land have become free from malaria.