BLOOD-INHABITING FLAGELLATES IN GENERAL 245 



the four stages. It is transmitted by cannibalism or by contamina- 

 tion, ingested cysts in the leishmania stage being infective. 

 Herpctoinouas (Fig. 15, C) is found in invertebrate and plant 

 hosts and may occur in any of the four stages, the predominating 

 one being herpetomonad. It is transmitted by the ingestion of 

 leishmaniform cysts or, in the case of plant-to-insect and insect- 

 to-plant transfer, by the ingestion or injection, respectively, of 



Cnd of fla^ellum •... 



^ndtilot^Ag M«ml» 



Fig. 15. — Comparative structure of the genera: A, Trypanosoma (T. 

 leivisi) ; B, Crifhidia; C, Herpctonwnas; D, Leishmania. (After Hegner 

 and Taliaferro.) 



herpetomonad individuals. ^Members of the genus Leishmania 

 occur in vertebrate and in invertebrate hosts. In vertebrates only 

 the leishmaniform type is found: in invertebrates and in cultures, 

 both herpetomonad and leishmaniform types are found. 



Three species of the genus Leishmania cause human diseases. 

 Three species of the genus Trypanosoma cause disease in man, and 

 a number of other species cause diseases in domestic and other 

 lower animals. Consequently these forms have been the subject of 

 considerable experimental study particularly regarding the chemo- 

 therapy of the diseases they produce, their mode of transmission, 

 their restrictions as to host, cultivation, and reaction of their hosts 

 to experimental infection. 



