EYES AND LIGHT 



231 



not at all. In this 

 way some tiny pic- 

 ture of a portion of 

 the outside world is 

 formed inside of each 

 of the many eyes, and 

 thus a mosaic of im- 

 pressions is produced 

 on nerve cells of the 

 animal's brain. 



The images pro- 

 duced in the parts of 

 the compound eye of 

 an insect or a lobster 

 are probably not very 

 distinct; but as the 

 animal gets many 

 simultaneous views 

 from somewhat dif- 

 ferent angles (a com- 

 pound eye may have 

 from twenty to sever- 

 al thousand separate 

 facets), the organ is 

 excellently adapted to 

 detecting slight move- 

 ments. In insects the 

 eyes are immovable, 

 but most of them are 

 able to see the move- 

 ments of an object or 

 of a light from prac- 

 tically all directions, 

 though not at a very 

 great distance. 



FIG. 95. Light-perceiving organs among the 

 mollusks 



In the scallop, A, and in other bivalves, there is a row of 

 eyespots along the edge of the mantle. In the snails, , 

 there is a more developed eye, frequently on the end 

 of a stalk. The octopus, C, has a pair of eyes similar in 

 many respects to the eyes of backboned animals 



