Color and spatial antagonism in the visual system of the larval swallowtail butterfly.

Many neurons exhibiting an antagonistic interaction between signals from one particular stemma (center) and neighboring stemmata (surround) were found in the second optic neuropil (medulla) of the larval swallowtail butterfly. Furthermore, most of the neurons showed a color opponent interaction in the center: combinations of opponent colors were blue vs green, UV vs green, and blue vs UV + green. Thus, photoreceptor signals are integrated into chromatically and spatially antagonistic mechanisms, even in the invertebrate.