1. Electrical threshold curves have been obtained for the stimulation by square and saw-tooth pulses of peripheral melanophore-aggregating nerve fibres in the minnow, Phoxinus. The responses show complete independence of pulse repetition rate over a wide range.
2. The results of von Gelei on the electrical stimulation of the spinal cord in ergotamine-treated minnows have been confirmed but it is found that the melanophore-dispersing activity may pass forwards or backwards from a stimulating electrode at any level of the spinal cord.
3. Identical results have been obtained for melanophore-aggregating activity in non-ergotized fish. All the spinal responses are slow and incomplete at repetition rates below 10/sec.
4. Von Gelei's arguments for mapping the pathways of melanophore-dispersing nerve fibres are shown to be insupportable.