Figure 2. Fluid flow in the development of the body plan.

(i) Polarity establishment in C. elegans. Anterior is at the left. Some component of the asters of the sperm pronucleus induces relaxation of cortical tension at the posterior end of the egg (A). This induces a movement of contractile elements from this end [curved arrows in (B)], and a simultaneous flow of cytoplasm towards this [straight arrow in (B)]. (C) P granules (black circles) are segregated to the posterior end of the egg by the cytoplasmic flow. (ii) Left-right development in vertebrates. Node of the mouse embryo (a) and leftward transport of microbeads by the cilia induced nodal flow (b). (i) © Hird and White, 1993. Originally published in (Hird, 1993). (ii) (A) (from Vogan and Tabin, 1999) and (B) (from Nonaka et al., 2002) are reprinted by permission of Macmillan Publishers, Ltd.