152 



BIOLOGY OF THE PROTOZOA 



3. Cilia.— Cilia are the motile organs of Infusoria and accompany 

 the most highly differentiated types of cortex to be found in the 

 Protozoa. Individually they are shorter, more delicate and less 

 powerful than flagella and owe their importance as motile organs 

 to their large numbers and synchronous beating. Their action 

 may be compared with that of oars in rowing, while flagellum action 

 might be compared with sculling, and the results of cilia and flagella 

 activities bear a relation similar to that between a racing shell and 

 a gondola (Fig. 81). 



Fig. 82. — Cilia structure. Axial filaments protruding from protoplasmic sheaths 

 in cilia of (1) Coleps hirtus, (2) Paramecium; (3) cilia make up of three lateral cirri 

 of Stylonychia. Silver line technique. (After Klein, Archiv f. Protistenkunde, 

 1929, courtesy of G. Fischer.) 



According to the interpretation of several observers, mainly 

 Schuberg, Maier, Schubotz, Schroder, etc., the cortex of ciliates is a 

 composite of zones of differentiated protoplasm. In the majority of 

 cases such zones cannot be made out, for one shades into the other, 

 and the whole into the alveolar endoplasm. In favorable cases, 

 however, we can distinguish: (1) A superficial periplast perforated 

 for the exit of cilia and trichocysts when present; (2) an alveolar 



