Abstract
Jumping behaviour (pyokori) which was elicited by a momental decrease of light intensity in the bw; st ss strain was markedly influenced by intensity of illumination, light wavelength and age of fly. Besides, an intimate relationship was found between the facet number and the pyokori response. B; bw; st ss strain was synthesized by the cross between Bar-eyed mutant and the original bw; st ss strains. The synthesized B; bw; st ss strain showed almost no pyokori response and the facet number of the strain was 35.7 in females and 63.9 in males. The heterozygous female flies from reciprocal crosses between B; bw; st ss and bw; st ss strains, showed 20-40 percent pyokori response and their facet number was about 270. The facet number of B; bw; st ss flies was increased to nearly the same as that of the original bw; st ss flies, when the larvae were bred by the medium containing 1.8 percent of lactamide. Flies, having enlarged eyes artificially, showed the similar pyokori response as the original bw; st ss flies. The frequency of pyokori response of B; bw; st ss flies became higher in proportion to the increase of facet number.
