Fig. 2. Schematic of an aesthetasc or mechanoreceptor sensillum on a downward flicking flagellum rotating at angular velocity relative to its base (see Fig. 1). The fluid velocity approaching the flagellum, U_yf, generates components U_ns=U_yfcos and U_ts=U_yfsin along the normal (n_s) and tangent (t_s) to the sensillum, where =–.