Regional Specialization for Control of Ocular Movements in the Compound Eyes of a Stomatopod Crustacean

1. Regional specialization within the triple compound eyes of the gonodactyloid stomatopod Conodactylus oerstedii (Hansen) was studied by examining how ocular tracking of a small target was affected after occluding vision in particular ommatidial regions with black enamel paint. 2. Complete occlusion of one eye did not prevent the other eye from tracking, indicating that the two eyes act somewhat independently. However, following such treatment, the angular extent over which the seeing eye moved while tracking was reduced. 3. An eye was able to continue tracking a moving target even after occlusion of the anterior tip or after painting over all of its posterior surface except the anterior tip (restricting the visual field to a patch about 40° in diameter). Similarly, occlusion of only the midband, the medial half or the lateral half of an eye did not prevent tracking. 4. Tracking was also possible, although with decreased amplitude, when either the dorsal or the ventral hemisphere was occluded. However, when both the dorsal and ventral hemispheres were occluded, leaving only the midband for vision, the ability of an eye to track was abolished. 5. A computer model was used to investigate whether the midband alone had the potential to direct tracking in our experiments. The model's output predicts that, in spite of its restricted field of view, if the midband is oriented within 20° of the horizontal, an eye could track using the midband alone. Conditions favoring such potential tracking occurred in our experiments, but neither tracking nor targetting movements were observed. 6. We conclude that ommatidia of the dorsal and ventral hemispheres of each compound eye are essential for ocular tracking in G. oerstedii. The midband appears to play no major role in this activity.