8 PROTOZOAN PARASITISM 



projected flagellum of spiral or screw-like move- 

 ment. 



Some flagellates have very pliable bodies, so that 

 they may twist and turn and so force their way among 

 solid materials in their liquid mediums by paths 

 smaller than their bodies. Such pliable bodies give 

 a darting action to the organisms. Others have very 

 rigid bodies of unchanging contour. Some are twisted 

 so that forward movement occurs in spirals. 



Another specialized organelle of locomotion is the 

 undulating membrane. This is a fin-like affair ex- 

 tending for various distances over the surface of the 

 body. It has a stiffening rib, similar to the core of a 

 flagellum and having a similar origin, which raises 

 up a covering of ectoplasm to form a ruffle. The 

 undulating or snake-like motion of this stiffening rib 

 and ruffle-like covering furnishes a means of rapid 

 motion. In a sluggish individual the slow undulation 

 of this ruffle has been confused by some with pseudo- 

 pod projection and has led to the report of an undu- 

 lating amoeba (Avioeha undulans, Castellani). 



Still another apparatus for locomotion and for 

 feeding is a surface covering of cilia (eyelid). Cilia 

 are comparatively short hair-like bristles which cover 

 the bodies of the ciliates. They move in rythmic 

 order like standing grain in a wind or the feet of a 

 thousand-leg, creating currents to propel the organ- 

 ism or to sweep food materials into reach of the in- 

 gesting surface. 



The different external appendages of protozoa, 



