STUDIES OF THE BRAIN, SENSE ORGANS AND LIGHT SENSITIVITY OF A BLIND CAVE FISH <i>(TYPHLOGARRA WIDDOWSONI)</i> FROM IRAQ

Abstract

SUMMARY The structures of the brain and sense organs of Typhlogarra widdowsoni , a blind cave fish from Iraq, are described and compared with those of Garra rufa , the nearest related species. In Typhlogarra the optic lobes and eyes are very regressed. Only the lateral parts of the optic tectum are developed and these incompletely. The optic nerves do not connect with the brain and the different parts of the eye are not easily recognisable. Experiments on the light sensitivity showed that Typhlogarra is slightly photonegative, but indifferent to the wave length. It is quite unlike Caeco‐barbus geertsi , a, blind cave fish from the Belgian Congo, which is markedly photonegative. Other differences in behaviour are also considered More general comparison of Typhlogarra with other blind species re‐emphasises that such fishes are remarkably diverse in their biology.