, pl. flagella A whiplike locomotory organelle of constant structural arrangement consisting of nine double peripheral microtubules and two single central microtubules; it arises from a deeply staining basal granule, often connected to the nucleus by a fiber, the rhizoplast. Although characteristic of the protozoan class Mastigophora, comparable structures are commonly found in many other groups, e.g., in sperm. [L. dim. of flagrum, a whip]