THE MOTIONS OF ANIMALS 



67 



one direction, then stop and flow the opposite way. It 

 is not easy to understand the exact method by which this 

 motion is produced. 



In some of the Protozoa, instead of the whole or a large 

 part of the body taking part in an ill-defined movement, 



3 



Fig. 35. — Amceba sp. ; showing the forms assumed by a single individual 

 in four successive changes. (Greatly magnified; from life.) 



there are definite organs of motion. Small, hair-like parts 

 of the body, called cilia or flagella, are extended into the 

 water and struck or pushed against it. Among the ciliate 

 and flagellate Protozoa we find some with the body cov- 

 ered all over with cilia, as in Paramcecium (fig. 36), and 

 some with only very definite cilia-covered areas, or even 

 with but one or two cilia, these being usually long and 



