Dorsal-lateral view of a Drosophila melanogaster embryo, anterior is bottom-left. Tracheal system is shown in white, tracheal tip (terminal) cells are shown in red, and cell junctions are in green. Tracheal tubes (white) form a complex network of hollow branches that deliver oxygen throughout the embryo. Tip cells (red) form long intracellular extensions that reach distant tissues to fulfil this function.