THE DRAWBRIDGE. 299 



would mate, under usual conditions, the optical axis take 

 this direction. To me it seems impossible to exphiin the 

 constant revolution of the eyeball on any otlier hypoth- 

 esis except that given, viz., that the optical axis extends 

 forward instead of sidewise. 



" When a fish wishes to eat anything, either at the bot- 

 tom of the pond or at the surface of the water, it swims 

 directly towards the object ; and in this case the eyes are 

 instantly adjusted in line with the body, so as to bring 

 the image of the particle desired upon the posterior por- 

 tion of the retina. In this case they lose their usual 

 liorizontal position. 



"If a fish wishes to turn to the right or left in the wa- 

 ter, the first movement is that of the eyes in unison with 

 the direction of the turning. This would be entirely 

 unnecessary if the apparent axis was the axis of most 

 distinct vision, as one of the eyes would see all that was 

 to be seen on the side of the turning. After this move- 

 ment of the eyes the body turns enough to bring the 

 eyes into their normal position ; then there is again a 

 movement of the eyes, and next a movement of the 

 body. This causes a peculiar jerking motion of the eye- 

 balls during the whole time of the turning of the body." 



The little sunfish that I had been noticing made ex- 

 cellent use of their wits as well as eyes, and eluded my 

 best-laid schemes to capture them. They knew perfect- 

 ly well that when in the crevices of the pier they were 

 safe, and that safety was an uncertainty under any or- 

 dinary circumstances. I waited many minutes for them 

 to reappear, and found that they only purposed showing 

 themselves after due precautions had been taken. They, 



