A number kept in an aquarium with a median partition, in which there was a small opening, were readily able to perceive the opening, swimming directly for it when opposite it. This observation is in direct contrast to their inability to perceive solid substances in their path. A sharp tap on the sides of an aquarium in which six blind fishes were swimming, where they had been for a number of days undisturbed, in a dark room, caused nearly all of them to dart rapidly forward. A second tap produced a less unanimous reaction. This repeated on successive days always brought responses from some of the inmates of the aquarium. Those responding were not necessarily the nearest to the center of disturbance, but sometimes at the opposite side of the aquarium or variously distributed through it. After a few days the fishes took no notice of the tapping by any action observable in the artificially lighted room.
Such tapping on a well-lighted aquarium containing both Chologaster and Amblyopsis was always perceived by the Amblyopsis, but the only response from these imperturbable philosophers was a slight motion of the pectorals, a motion that suggested that their balance had been disturbed and that the motion was a rebalancing. Chologaster, on the other hand, invariably darted about in a frantic manner. One individual of Amblyopsis floating on the water was repeatedly pushed down by the finger without being disturbed. If, however, they are touched on the side they always rapidly dart away.
From everything observed, it is quite evident that Amblyopsis is not keener in perceiving objects or vibrations than other fishes, and ordinarily pays much less attention to them. Whether it possesses a greater power of discrimination of vibrations it would be difficult to say. It certainly possesses very elaborate tactile organs about the head. These tactile organs are probably more serviceable in detecting and precisely locating prey in the immediate neighborhood than for anything else. Some observations on young Amblyopsis are of interest in this connection.
The young, with a large amount of yolk still attached, show a well-developed sense of direction. A needle thrust into the water near their heads and in front of them causes a quick reaction, the young fishes turning and swimming in the opposite direction. They will do this two or three times, then, becoming exhausted, will remain at rest. Sometimes an individual will not move until it is actually touched by the needle. The needle must come within about three or four millimetres of the fish before it is noticed. Then, if it produces any result, it causes the fish to quickly turn and swim some distance, when it falls to the bottom again and remains