The refractive index 1.8 is, however, less likely for the
insect corneal lens, because it is widely accepted that the
refractive index of insect chitin is 1.5–1.6 (e.g., Dethier,
1942). A high apparent refractive index was reported for
corneal lens in some arthropods; 1.67 for the posterior
median eye of Dinopis subrufus (Blest & Land, 1977) and
1.60–1.64 for two species of New Zealand harvestmen
(Meyer-Rochow & Liddle, 1988). The apparent refractive
index 1.8, as predicted from the data in the present study,seems to be much higher than values reported in those previous
works. A high apparent refractive index estimated in
the present study must therefore be achieved by some
higher-order organization of the lens.