86 BLIND VERTEBRATES AND THEIR EYES. 



Chologaster papilliferus detects its food entirely by the sense of touch. Two 

 which were kept in an aquarium for over a year were starved for a few days. They 

 became very nervous, continually swimming along the sides of the aquarium. Some 

 individuals of A sell us were introduced. These, though quite near, produced no 

 effect if moving in front of Chologaster. The moment one came in close proximity 

 to a fish from any direction, by a flashlike motion it was seized. None of them 

 were swallowed. The fishes became very alert after the introduction of the sowbugs 

 and when swimming forward would strike at a part of a leaf if it came in contact 

 with the head of a fish. It seemed evident that the eye gave no information of 

 the character of the object. As the Asellus was not altogether to their taste, Gam- 

 imirus was introduced. One of these, swimming rapidly toward the chin of the 

 Chologaster from behind and below, was instantly seized when it came in contact 

 with the fish. The eye could not have located the Gammarus at all. The action 

 is in very strong contrast to the action of such a fish as Lepomis, which detects its 

 food by sight. It is undoubtedly this peculiar method of locating and securing 

 food which has enabled the Amblyopsidae to establish themselves in caves. 



On March 20 the eyes were removed from 7 living specimens of Chologaster 

 papilliferus with the following results: 



Within half an hour after removing the eyes, examples of Asellus were intro- 

 duced into the aquarium, which were readily detected and captured. In captur- 

 ing them the chologasters were not as accurate as fishes might be expected to be 

 that do not ordinarily depend on their eyes to help in locating prey. It may be 

 borne in mind, however, that the eyes were removed from the surface and that in 

 addition to the removal of the eyes some of the tactile organs were probably dis- 

 turbed or destroyed. 



A rod held in the hand was readily perceived by the blinded fishes, who avoided 

 it with as much dexterity as an Amblyopsis would, except that their actions in 

 avoiding the rod were very much quicker than the action of an Amblyopsis. The 

 latter, if approached from in front, will back water with its pectorals and then, if 

 the rod comes nearer, it will turn to one side or another, frequently with lazy delib- 

 eration. Chologasters, on the other hand, would turn tail with a flashlike motion 

 when the stick was approaching them. They could be approached from the back 

 more readily than from other regions. 



The action of the blinded fishes was in this respect precisely like that of an 

 unblinded one in the same aquarium. Removing the eyes makes no appreciable 

 difference in the appearance of the fish, and a number of colleagues were asked 

 whether the fishes were detecting the rod by sight (with the eyes) or by tactile 

 sensation. Not knowing that the eyes had been removed, the verdict, in the major- 

 ity of cases, was in favor of the eyes; in the other cases it was doubtful. There 

 was no general disturbance of the fishes in the aquarium when the rod was intro- 

 duced. Only the ones immediately concerned responded. 



On April 4 I was able to touch each of 5 blinded chologasters on the snout 

 with a glass rod before it made any attempt to get away. The same is true of some 

 which had not been blinded. 



The blinded chologasters readily swim about in the aquarium, regardless of 

 protection or of contact with the sides of the aquarium. They not infrequently 

 lie at the bottom, but the general tendency is to swim about freely. One of them 

 lived for 2 years after the operation. 



