Integration of Colour Signals in the Medulla Of the Swallowtail Butterfly Larva

Spatial and chromatic properties of 25 types of medulla neurones which integrate input from different optical units (stemmata) of the larval eye in the swallowtail butterfly were examined by illuminating individual stemmata with chromatic stimuli. Eleven neurones received different types of colour (opponent) input from a few stemmata; thus, the receptive fields are spectrally heterogeneous. The stemmata dominating these complex neurones were usually located in the frontal (central) region of the eye. Seven neurones showed a relatively homogeneous spectral profile over the receptive field by receiving similar spectral input from two or three stemmata which were usually located in the dorsolateral(peripheral) region of the eye. Three of these simple units showed tonic or phasic responses. The remaining seven were also spectrally simple neurones but with larger receptive fields covering four to all six stemmata. Some units showed a spatial summation of responses or a spatial antagonism between central and peripheral or dorsal and ventral regions of the eye.