1. The colour of the minnow Phoxinus phoxinus L. and its ability to undergo colour change were studied after partial and complete blinding. The blinding was accomplished either by section of the optic nerve or by tectal ablation.
2. Following bilateral section of the optic nerve the blinded minnows darken. After the initial darkening, half of the fish pale and the other half remain dark.
3. The colour of the fish blinded by bilateral section of the optic nerve could not be affected by external conditions.
4. Following complete removal of the optic tectum the fish at first paled, but after 24 h they darkened to very variable tints.
5. Unilateral section of the optic nerve coupled with unilateral tectal removal on the same or opposite side did not affect the ability of the fish to change colour.
6. The bilateral removal of the anterior tectum from a blinded darkened fish did not affect its colour.
7. The bilateral removal of the posterior tectum of a darkened fish caused maximal pallor.
8. By a series of lesions an area in the dorsal posterior part of the optic tectum was found to cause darkening in the blinded fish because following its removal the fish paled.
9. It is suggested that the fibres from the tectum may act by exciting or inhibiting the neurones of the paling centre in the anterior medulla.
The work presented here was part of the work approved by London University for the Degree of Doctor of Philosophy.
- Copyright © 1971 The Company of Biologists Ltd.