Fig. 9. The mapping of burrow distance onto the ommatidial array. Shown is the visual field of a crab that is (A) 10 cm, (B) 20 cm or (C) 30 cm away from its burrow. The burrow location is marked by a grey circle. The labelled contour lines within each plot correspond to positions in space that have a fixed distance from the crab's burrow. Contours have been drawn for 5, 10, 15, 20, 25, 30, 40 and 50 cm. The solid black lines show the retinal path of a set of two fictitious dummies that approach the burrow from a distance of 50 cm and move either directly over the crab's burrow or move 10 cm past the burrow. In contrast to the previous figures, elevation has been transformed into facet rows. The x-axis (azimuth) scale has been adjusted such that individual ommatidia would take up equal space along the x- and the y-axes. These transformations reduce but do not eliminate the effect of perspective foreshortening. The white arrows in C show the local directions of the distance to burrow gradient on the eye.

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