161 



Aquatic JLitt 



fish is endowed is at present an unsolved 

 riddle ; but it is certain that his be- 

 havior complex is of very different pat- 

 tern from ours and whatever mind he 

 may have would surely be as different 

 as the pattern of his sense experience is 

 different. 



Let us pursue this line of inquiry 

 further and review what is known of 

 the other senses of our catfish. This fish 

 has small and poorly developed eyes and 

 is largely nocturnal in habit, lying con- 

 cealed in dark corners during the day. 

 The retina has remarkable powers of 

 adaptation to differences in illumination 

 and the fish is very sensitive to changes 

 in intensity of light. But the eye is not 

 the only light-sensitive organ. Experi- 

 ments with blinded fish show that the 

 entire skin surface is sensitive to differ- 

 ences of light intensity, a not uncommon 

 feature of aquatic animals. The image- 

 forming power of the eye is probably 

 not very good. Some catfishes, it is true, 

 will take a spoon hook, and probably a 

 bait must always be in motion if it is 

 to be sensed by the eye. The usual 

 method of feeding is to trail the bottom 

 with the barblets, which are very ef- 

 ficient organs of both touch and taste, 

 and when contact is made with a worm 

 or other suitable food to turn sharply 

 and snap it up. 



Just as the eyes are supplemented in 

 their functions by the skin, which has 

 a very feeble sensitiveness to light, so 

 the highly refined chemical sense organs 

 in the nose and taste buds are also sup- 

 plemented by a chemical sense in the 

 general skin. In some other fishes which 

 have been carefully tested the general 

 skin surface is found to be very sensitive 

 to chemicals in solution, to some sub- 

 stances more sensitive, in fact, than are 

 the taste buds themselves. 



In fishes, as in men, the ear contains 



two quite different sense organs — the or- 

 gan of hearing and the organ of the 

 sense of equilibrium. The latter lies in 

 the semi-circular canals, which in form 

 and function are similar to those in the 

 human body. Indeed, the semi-circular 

 canals probably play a larger part in the 

 behavior of the fish, since maintaining 

 perfect equilibrium is a more difficult 

 matter for a fish suspended in water of 

 about the same specific gravity as the 

 body than for a man walking on solid 

 ground. But when the man essays to fly, 

 his semi-circular canals again take a 

 dominant place in his sensory equipment. 

 In the practical testing of the fitness of 

 men who are candidates for the Air 

 Service of the Army the most important 

 point to be determined is whether the 

 semi-circular canals are functioning nor- 

 mally. 



Whether fishes hear at all has been 

 hotly controverted. That they are very 

 sensitive to mechanical jars and vibra- 

 tions all agree, but it has been difficult to 

 prove whether their responses to these 

 vibrations are brought about through 

 their ears or by refined cutaneous sensi- 

 bility. The ingenious/ experiments of 

 Parker have shown that both of these or- 

 gans serve and that, in fact, fishes do 

 hear true sound waves of rather low 

 pitch with their ears. To tones of high 

 pitch they are deaf and probably they 

 have no power of tone analysis, that is, 

 they can hear a noise but cannot tell one 

 tone from another. 



The fishes can boast no superiority 

 over ourselves in being able to respond 

 to low tones by both the ear and Lhe 

 skin. We can do the same, as can read- 

 ily be shown by lightly touching the 

 sounding board of a piano or organ when 

 a low tone is struck. The same tone 

 heard by the ear can be readily felt by 

 the finger tips. But for perceiving still 



