84 Instinct and Intelligence 



of many eyes, each with its own retina and 

 dioptric apparatus separated from its neigh- 

 bours by pigment-cells. 1 



The visual power of these beings depends 

 largely on the form and the number of facets 

 possessed by the outer surface of their eyes; 

 for instance, the prominent convex eye of the 

 dragon-fly is said to contain from 12,000 to 

 17,000 facets. We can form an idea of the 

 acuteness of vision possessed by these insects 

 if we try to catch one of them when hovering 

 over a pond. The dragon-fly will allow us to 

 approach our net just near enough to miss 

 catching it, when off he darts, seeming able to 

 measure the length of the handle of our net, 

 for the insect repeatedly flies oft in spite of 

 our efforts to capture it. Wasps can judge the 

 size and colour of inert objects by the aid of 

 their eyesight. Thus if some dead flies are 

 placed together with other insects on a table in 

 a room where there are wasps, a wasp will soon 

 fly down and without hesitation alight on a dead 

 fly, which he will carry off, and this process is 



1 R. H. Burne, Asst. Curator, Roy. Coll. Surgeons of England, 

 Cat. K.C.S. Museum, Physiol. Series, Vol. III., p. 302. 



