120 PHYLUM. PROTOZOA—THE SIMPLEST ANIMALS. 
Protozoa and Disease.—The discoveries of recent years 
have shown that the study of Protozoa is an inquiry 
of great practical importance. Numerous Protozoa— 
representing the main divisions of the group—are known 
at some stage of their life history to be parasitic in the 
human body or in domestic animals. Some of them 
are associated with serious and fatal diseases. Thus, 
Amaba (Entameba) histolytica causes an inflammation 
of the intestinal mucous membrane and liver abscesses. 
Several flagellates of the genus Zrypanosoma are serious 
Fic. 53.—Glossina palpalis, tse-tse fly. 
parasites of the blood affecting man, horses, cattle, 
camels, and other domestic animals in both the old 
and new worlds. TZ7ypanosoma gambiense (Fig. 54) is 
the parasite causing the fatal “sleeping sickness,” a human 
disease disseminated by tse-tse fly, Glossina palpalis, in 
Africa (Fig. 53). In the fully formed Trypanosome, the 
flagellum is expanded into an undulating membrane 
which extends down the edge of the cell. In this 
membrane there are eight fine contractile threads or 
myonemes, which are connected at the lower end with 
a modified nucleus called the blepharoplast. The so- 
