1. Cauterization of the region of the optic chiasma causes the permanent expansion of the melanophores. Subsequent cauterization of the eye has no further effect.

2. Severance of the optic nerve or damage to the eye itself results in the cessation of the chromatic response to illumination and background.

3. Specimens operated upon in this manner do not lose the melanophore response to moisture, contracting in dry and expanding in moist conditions.

4. Only a slight residual primary response can be detected.

5. The implications of these results in relation to chromatic control are discussed.

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