68 The Microscope. 



multiplied; yet something will generally be found 

 answering to the lens, the retina, and the pigment. 



The eyes of the dragon-fly, cricket, and lobster, 

 all resemble each other in being composed of a very 

 great number of minute lenses joined into a single 

 group, each one of these lenses being (according to 

 the best naturalists) "a distinct organ of vision." 

 The lenses are arranged side by side in a form that 

 allows of their being close together without loss of 

 room. 



If they were in circles a great deal of space would 

 be wasted, and so there would be also were they 

 eight-sided. But they are usually formed with six 

 sides, just the same shape as the cells in a honeycomb, 

 so that no room whatever is lost. Naturalists have 

 counted twelve thousand lenses in each eye of the 

 dragon-fly. These lenses can be mounted in such a 

 way that they will keep their shape. 



It may sound like a difficult thing to count so great 

 a number ; but they are arranged with such extreme 

 regularity that their amount is readily calculated. 

 Magnified 36 diameters, they are like a piece of lace ; 

 and there is another thing which they also much re- 

 semble the wire-netting that is often put round 

 garden plots to keep out rabbits, just like gigantic 

 lace with holes about the size of half-crowns. 



Let us imagine an. experiment with a piece of this 

 wire-netting. Suppose we should provide ourselves 

 with several dozens of round spectacle-glasses, and 

 set one in each of these holes, and hold the piece of 

 wire-netting at a certain distance from a wall the 



