THE SIGHT OF INSECTS 127 



in which the feather was placed, the smallest fraction of an inch 

 beyond the eye window. It is clear and in perfect focus, even show- 

 ing the smallest scales of the feather in fine detail. In each successive 

 experiment the feather was moved perhaps one micron further from 

 the eye, the result being that its plumes rapidly lost focus until all 

 detail was gone. This was in no way due to the use of a too powerful 

 lens, as proved by the fact the feather remained in fair focus when by 

 itself at a similar distance from the lens, only becoming blurred when 

 viewed through the cuticular windows of the eye. 



From these not over-difficult experiments we have the following 

 facts concerning the power of sight in insects. In the first place they 

 see objects in mosaic patterns. Objects are seen in clear focus only 

 when extremely close to the eye. At greater distances, only the out- 

 line of the object is visible and beyond a few inches things doubtless 

 pass into mere shadows with intervening patches of light. 



Further the experiments tell us that an insect cannot always depend 

 upon its eyes. To find its mate, and to sustain life, by securing food, 

 it must rely upon the sense of smell. But what of the fly who even 

 with its defective eyesight, still avoids your swat so easily? True, he 

 cannot see you in clear outline, but remember that you appear to him 

 as a gigantic shadow more reaching than that cast by a range of lofty 

 mountains. When you make your swat, this great shadow topples 

 toward him with fearful speed, but Nature has supplied the creature 

 with eyes that exaggerate and a speed that excels a falling avalanche. 

 ^ Now it might be argued that these experiments were not really per- 

 formed with the actual eye of an insect, but simply with the outer 

 coating of that organ, and therefore prove nothing. Perhaps, in part 

 such a statement w r ould be true, yet is it not the outermost window 

 that governs the quality of sight? A man might possess perfect 

 vision, yet were he to stand with his face against a dirty window his 



