﻿104 BLIND VERTEBRATES AND THEIR EYES. 



The large aquarium rested on a masonry pedestal, which eliminated all vibra- 

 tions of the tioor. The small one was suspended by cords running from one side 

 of the room to the other. 



After various trials with small tuning-forks which produced vibrations between 

 ICG and 512 per second, which gave negative results, I used a large fork 12.5 inches 

 in length vibrating 100 times per second and which produced a large volume of 

 sound. 



I used (a) unmaimed blind fishes and (b) others whose auditory nerves had 

 been cut. I also attempted work with fishes whose lateral line nerves and nerves 

 to the skin had been cut, but the specimens either died or did not revive suffi- 

 ciently to get normal reactions. 



(a) Unmaimed blind fishes when placed in the aquarium in\ariably dart to the 

 bottom and remain there for a short time, after which they begin to swim about 

 rather rapidly. They soon become more quiet if nothing further disturbs them, 

 but continue swimming about in a leisurely way, stopping now and then for a few 

 seconds at a time. After they have been in the aquarium for 12 or 24 hours, these 

 stops are more frequent and longer. The fishes strike various attitudes during 

 these stops, but they seldom rest upon the bottom. Instead they are usually poised 

 as if ready to dart away. The body seems so well balanced that they have no trouble 

 in maintaining any position they may happen to take. During these stops the tail 

 always projects straight backward and the pectoral fins stand at right angles to the 

 body. If at this time the sounding board is caused to vibrate, the fish responds 

 either with a quick movement of both the tail and pectoral fins or by the pectoral 

 fins alone. Twenty fishes were each subjected to 5 tests, and out of the 100 trials 

 there were 97 responses and 3 failures. 



(b) Fiindiilus, with the auditory nerves cut, acts as normal blind fishes do in 

 swimming slowly or in resting, but when stimulated, loses entire control of its 

 equilibrium. Parker suggests that in resting or swimming slowly the fish depends 

 upon the eye for orientation, but in quick movements the ear comes into play. The 

 reactions of Amblyopsis seem to support this suggestion, for with both auditory 

 nerves cut they have no control of their orientation. When resting, they lie on the 

 side or back, either at the surface or on the bottom. In swimming slowly they 

 sometimes move forward in irregular lines, but when they attempt rapid locomotion, 

 they move in irregular spirals about the long axis of the body and make no progress 

 one way or the other. With only one auditory nerve cut the movements are quite 

 different. The fish is able to move forward, but it goes in a corkscrew-like path, 

 turning over on its axis as it swims along. The same result was obtained by 

 Eigenmann by thrusting a pin into one of the auditory organs. 



The operation of eliminating the ear is a comparatively easy one to perform. 

 Of those operated on, more than half recovered. They generally lived for 2 or 3 

 weeks, and some even longer. The observations were made from i to 2 days after 

 the operation. With these fishes three kinds of responses were obtained. If they 

 were perfectly quiet when the sounding board was caused to vibrate, they either 

 responded by a slight movement of the pectoral fins or by a movement of both 

 caudal and pectoral fins. If, on the other hand, they lay with the body quiet and 

 with the pectoral fins moving slowly when the sounding board was caused to 

 vibrate, they responded by stopping the fin movements. Ten fishes were each 

 subjected to 10 tests, and out of 100 tests there were 96 responses. This result 



