SIGHT IN INVERTEBRATES 165 



The pigment and the reflecting wrappings round each 

 ommatidium ensure that only Hght that passes straight down 

 the centre of the tube reaches the Hght-sensitive cells at the 

 bottom — any rays coming in from the sides are cut off. Thus 

 no image is formed at the bottom of the tube, and the cells 

 there register only the intensity of the light that reaches 

 them. The image of the surroundings is therefore built up 

 from an enormous number of separate dots of differing 

 intensity, like a photograph printed in a newspaper by the 



-CRYSTALLINE LENS 



-CRYSTALLINE CONE 

 PI6MENTCELL 



-RETINAL CELL 

 — PI5MENTCELL 



Fig. 9. A single ommatidium from the eye of a Honey Bee highly magnified. 



"half- tone" process. A picture built up like this resembles 

 a mosaic, and consequently this kind of eye produces mosaic 

 vision, as explained in Chapter II. 



It has sometimes been thought that each ommatidium 

 produces an image, and that an insect sees by "mentally" 

 fusing into one the thousands of separate pictures thus 



