90) THE BEAUTIES OF NATURE | cnHap. 
“compound” eyes one on each side of the 
head, have between them three small ones, 
known as the “ ocelli,” arranged in a triangle. 
The structure of these two sets of eyes is 
quite different. The ocelli appear to see as our 
eyes do. The lens throws an inverted image 
on the back of the eye, so that with these 
eyes they must see everything reversed, as we 
ourselves really do, though long practice 
enables us to correct the impression. On the 
other hand, the compound eyes consist of a 
number of facets, in some species as many as 
20,000 in each eye, and the prevailing 
impression among entomologists now is that 
each facet receives the impression of one 
pencil of rays, that im fact the image 
formed in a compound eye is a sort of 
mosaic. In that case, vision by means of 
these eyes must be direct; and it is indeed 
difficult to wnderstand how an insect can 
obtain a correct impression when it looks at 
the world with five eyes, three of which see 
everything reversed, while the other two see 
things the right way up! | 
On the other hand, some regard each 
