Figure 3. Fluid flow implicated in organogenesis in mouse (A)–(C), zebrafish (D)–(J) and fruit fly (K)–(L) embryos.

(A)–(B) Flow of aqueous humour: first produced in the ciliary body of the eye, it circulates throughout the anterior part of the eye, and then exits primarily through the trabecular meshwork (Calera et al., 2006; Alward, 2003). (C) Flow of exogenously microinjected India ink in the mouse brain showing the direction of the cerebrospinal flow and the parallel neuroblast migration (Sawamoto et al., 2006). (D) Fluid flow in the central canal of the spinal cord in a zebrafish embryo (Kramer-Zucker et al., 2005). (E)–(F) Beating cilia and kinocilia in zebrafish ear during otolith seeding (Hammond and Whitfield, 2006; Riley et al., 1997). (G)–(H) Cilia in the pronephric ducts (arrows indicate the point were the pronephric ducts merge at the cloaca) and the associated flow through the pronephric kidney observed by injected dye into the circulation (Kramer-Zucker et al., 2005). (I)–(J) Valveless atrio-ventricular junction in the embryonic zebrafish heart indicating mean flow direction (red arrows) and streak-like imprints left by moving blood cells (Hove et al., 2003). (K)–(L) Liquid clearance and gas filling of a Drosophila embryo. The initiation of the gas filling (first gas bubble) and its completion, when all tracheal branches are gas filled, are shown (Tsarouhas et al., 2007). (A), (D), (E), (G) and (H) are reproduced with the permission of the Company of Biologists. (B) from Alward, 2003 and (C) from Sawamoto et al., 2006 are reprinted with permission of AAAS. (F) from Riley et al., 1997, (K) and (L) from Tsarouhas et al., 2007 are reprinted with permission of Elsevier. (I) and (J) are reprinted by permission of Macmillan Publishers, Ltd. (Hove et al., 2003).