CILIARY MOVEMENTS 



299 



motion. In our own body, for example, the movement 

 of the white corpuscles is a case in point. To this amoe- 



FiG. 129 — White corpuscles escaping from blood tube by amoeboid motions. 



bold movement these corpuscles owe their power to pass 

 through spaces in the walls of the blood vessels through 

 which the smaller but rigid, red corpuscles cannot pass. 



Ciliary movements. — Amoeboid movement is at best a 

 very slow method of changing position, and is interesting 

 mainly in showing us that free protoplasm has the power 

 of contractility. We should expect, then, to find in the 

 higher protozoans a more rapid 

 method of progression. Such 

 a modification in motile organs 

 we do find in many of the pro- 

 tozoans, and these organs are 

 called cilia. 



In the arcella, movement 

 is produced by pseudopodia 

 which are projected through an opening in the cell wall, and 

 these can be extended and withdrawn as necessity requires. 



-Shell 



^seudopod 



■■' 'vr>- 



An arcella creeping by 

 pseudopod. 



