Figure 3.

(A) Schematic image of Purcell’s scallop presenting a nonreciprocal motion in a high Reynolds number fluid and reciprocal motion in a low Reynolds number fluid with no net replacement (so-called “Scallop Theorem”¹⁴¹). (B) Summary of five strategies (S1–S6) to break the Scallop Theorem to produce an effective movement. S2 is reproduced with permission from refs (137 and 140). Copyright 2014, Brumley et al. This article is distributed under the terms of the Creative Commons Attribution License. S4 is reproduced with permission from ref (142). Copyright 2015 The authors. S5 is reproduced with permission from refs (137 and 140). Copyright 2014 Macmillan Publishers Limited. This is an open access article distributed under the terms of the Creative Commons CC BY license.