Fig. 7. Retinal position of all points in the visual field of a crab that are 25 cm away from the crab's burrow. The positions are shown for different crab-burrow distances (solid and dotted lines), as labelled. On these lines of equal dummy-burrow distances we marked the positions of dummies approaching from different directions with grey dots. The approach directions are grey-level coded, with smaller track angles being represented by progressively lighter greys (see inset). Note how the position of the burrow moves upwards in the visual field of a crab as it moves further away from its burrow (grey circles at 0° azimuth). The vertical line of small black dots along the y-axis indicates the elevation in which consecutive neighbouring vertical rows of ommatidia are facing, to show the pronounced increase in vertical resolution towards the horizon and the approximate level of resolution with which the dummies are seen by the fiddler crab eye (after Land and Layne, 1995a; Zeil and Al-Mutairi, 1996).