Some Reactions of the Ammocoete

1. Experiments are described which show that the threshold value for the light energy, which will initiate swimming movements in the ammocoete, is in the region of 3 foot-candles. 2. The part of the spectrum which is most active is in the green-blue region (0.55µ-0.4µ). 3. Ammocoetes are very strongly thigmotactic, the most sensitive region being the sides of the trunk. 4. Ammocoetes between 40 and 70 mm. long are not rheotactic. 5. The relation of these responses to one another and their relative importance to the ammocoete in its natural environment are discussed.