WHAT THE FISHES SEE 



fails. The land creature, living in air through which 

 the light passes without hindrance, can see a long way; 

 the water animal, bathed in water which scatters and 

 diminishes the light, has its powers of vision definitely 

 limited. Its surroundings hamper rather than aid it. 

 The basilisk's field of vision is limited to its immediate 

 surroundings, and can extend no farther. When I had 

 carried out experiments on this fish, with its coloured 

 plates of dissimilar hue, with regard to the visibility of 

 colours, I discovered that some, those of the blue section 

 of the spectrum, have hardly any effect on it, whereas 

 it is more sensitive to those of the red, and especially to 

 yellows and oranges. I tried to find out the distance at 

 which this sensibility is effective. Usually, nothing 

 could be noted beyond twenty-four to twenty-eight 

 inches ; and this was obviously the limit of the creature's 

 normal vision. Moreover, the impression was keener 

 when both eyes could observe together, and not so keen 

 when the vision was limited to one side. 



There was further evidence of the importance of 

 binocular vision in these remarkable little fishes. I 

 noticed that my finger, when I put it into the water near 

 them, interested and attracted them even if I kept it 

 still. They came out of their shelters, approached it, 

 and tried to nibble at it. But this only happened if I put 

 my finger directly in front of them; nothing happened 

 if I put it anywhere else. If I went forward on one 

 side, so that the finger could only be seen by a single 

 eye, I could see that eye turn and follow the movements 

 of my hand, but the head did not move; it was as 

 though it perceived the movements without realizing 

 the nature of the object. On the other hand, if I put 

 my finger in the water in front of both eyes, so that both 

 were attracted at the same time, there was no hesitation 

 about the reaction. The object was perceived and the 

 fish came out, drew near, and bit. 



The other species of blenny in the same tank, or in 

 neighbouring tanks, had nothing of the sort to show. 



