_Crithidia fasciculata_, the type species, was found by Léger in the alimentary canal of _Anopheles maculipennis_. Crithidia occur in bugs, flies, fleas,[122] and ticks. Some of them are found in the body-fluid of the invertebrate host as well as in the gut. Others may be restricted to the body cavity or intestine respectively. _C. melophagia_ from the sheep-ked, _Melophagus ovinus_, and _C. hyalommæ_ from the hæmocœlic fluid of the tick, _Hyalomma ægyptium_, pass into the ovaries and eggs of their hosts, and the young keds or ticks are born infected. [122] See Porter, _Parasitology_, iv, p. 237. _C. fasciculata_ has been shown by Laveran and Franchini to be inoculable into white mice, producing a sort of experimental leishmaniasis therein. In one case cutaneous lesions were produced like those of Oriental sore. Crithidia are natural flagellates of Arthropoda, with their own pre-flagellate, flagellate and post-flagellate stages, and must not be confused with transitory crithidial stages of trypanosomes. Genus. *Leishmania*, Ross, 1903. With an oval body containing nucleus and blepharoplast (kinetic nucleus) but no flagellum. An intracellular parasite in the vertebrate host. Included in the genus _Leishmania_ are three species, namely:-- (1) _Leishmania donovani_, Laveran and Mesnil, 1903, the parasite of Indian kala-azar, a generalized systemic disease, usually fatal, occurring in subjects of all ages. (2) _Leishmania tropica_, Wright, 1903, the parasite of Delhi boil, Oriental sore, Aleppo button--a localized, cutaneous disease, usually benign. (3) _Leishmania infantum_, Nicolle, 1908, the parasite of infantile kala-azar, occurring in children (and a few adults) around the shores of the Mediterranean. The disease is perhaps a form of Indian kala-azar, and the parasite is probably identical with _L. donovani_. These diseases may be termed collectively leishmaniases. The morphology of the various species is practically identical. *Leishmania donovani*, Laveran and Mesnil, 1903. Syn.: _Piroplasma donovani_, Laveran and Mesnil. The parasite of Indian kala-azar was demonstrated in 1900 by Leishman from a _post-mortem_ examination of a case of “Dum-Dum fever,” but details were not published till May, 1903. In July, 1903, Donovan found similar bodies from cases in Madras. Rogers succeeded in cultivating the parasite in July, 1904.[123] The original centre of the disease was probably Assam; it occurs also in Madras, Ceylon, Burma, Indo-China, China and Syria. A variety of this leishmaniasis is found in the Sudan. The patient becomes emaciated, with a greatly enlarged spleen. There is anæmia and leucopenia. [123] The literature up to 1912, on kala-azar and other leishmaniases is reviewed in the _Kala-azar Bulletin_. Afterwards in the _Tropical Diseases Bulletin_.