Fig. 5.

Comparison with various types of swimmers. (A) Efficiency of sperm-type swimmers, bacteria-type swimmers, and ciliates. Typical length ratio of human sperm and E. coli are indicated. Filled symbols represent the results of ciliates with optimal efficiency, while open symbols are the results of sperm-type or bacteria-type swimmers. (B) Number of cilia as a function of body length; optimal number of cilia (filled symbols) increases with ${\left(a/L\right)}^2$, which coincides with species of microalgae and ciliates found in nature (open circles).