Movement on dark–light adaptation in beetle eyes of the neuropteran type

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Abstract
Beetles of several species belonging to the families Carabidae, Dytiscidae, Gyrinidae and Hydrophilidae have an eye of the neuropteran type which is characterized as follows. In the dark-adapted state a long column formed by retinula cells (in these families numbering seven) stretches from the cone tip to the rhabdom layer. In the light a crystalline tract, formed from the outer layer of the cone, extends about 100 $\mu $m from the cone and is surrounded by pigment cells. Scarabaeid beetles examined are similar but lack the distal rhabdomere always found in the above groups. All have a basal retinula cell with rhabdomere. In the scarabaeids the retinula cell columns have a content of solids greater than the surrounding cells, suggesting that they act as light guides across the clear zone.

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