PROTOZOA IN THE DIGESTIVE TRACT 39 



result and not the cause of the diarrhoea. It is widely dis- 

 tributed, but more common in the tropics and subtropics. 

 The trophozoite only is known. 



Trophozoites 



1. Living specimens. This is an actively motile flagellate 

 (Fig. 10, 1) which shows a jerky or spinning movement. 

 It measures 5-20n in length. The organism is highly plastic, 

 and assumes various body forms in life. It is however gen- 

 erally ovoid or pyriform in body outline. Its anterior end 

 is usually rounded, while the posterior end often tapers 

 into a point through which the axostyle protrudes. A cyto- 

 stome is located close to the anterior tip. On the opposite 

 side of the body is seen the undulating membrane which 

 extends slightly spirally towards the posterior end. The 

 axostyle and undulating membrane are structures which 

 distinguish this flagellate from Chiloniastix mesnili (p. 36) 

 in life. Over a dark field condensor, the flagella become 

 clearlv visible. There are tvpically five flagella in all, 

 inserted at the anterior end of the body. Of these four 

 are equally long, directed anteriorly, and lash freely, while 

 the fifth flagellum makes the outer border of the undulating 

 membrane. After being on the slide for some time, or 

 when held stationary by debris in the preparation, the 

 organism may become rounded and the undulating mem- 

 brane becomes spread along the margin of the body and 

 continues to undulate. Such an individual may simulate 

 an amoeba. 



2. Stained specimens. The majoritv of the stained speci- 

 mens are more or less pyriform in shape, with the rounded 



