44 



THE PROTOZOA 



dopodia, the protoplasmic filaments, known as flagella and cilia, are 

 derived solely from the ectoplasm and are constant in their position, 

 and, save for the occasional absorption within the body, for some rea- 

 son or other, they are unchangeable. Flagella-motion, characterized 

 by energetic contractions or undulations, or by rotary motions, differs 



-**-* 



X" 





Pig. 15. Types of pseudopodia. 



A. AmxialimicoIaRhmb. [RHUMBLER.] B, Amoeba blatt<e Biitsch. [BiJTSCHLl.] C. Lieber- 

 kuhnia sp. [VERWORN.] D. Actinosphcerium Eich. Ehr. [ORIGINAL.] x, the axial filament. 



entirely from the slow flowing movement of pseudopodia; yet, as 

 Dujardin first observed, in some forms pseudopodia change into 

 flagella, and flagella into pseudopodia. In structure, flagella are long, 

 thin, usually pointed threads of protoplasm, which, as a rule, are 

 longer than the cell itself ; they are typically single, but there may 

 be two, three, or many. Cilia, on the contrary, are always multiple, 

 and are never interchangeable with pseudopodia (Fig. 16). Although 



