ia6 INSECT BEHAVIOR 



developed state. In order to understand what follows we must first 

 become acquainted with the typical insect eye. 



It is not the organ we generally think of, as one sees it in the head 

 of a man, a beast or bird, but a compound and vastly different object. 

 It is true that upon examining an insect closely we observe two large 

 eyes, one set on either side of the head, but if we were to magnify the 

 outer shell or cornea of these protrusi9ns, we would find that what 

 appears to be a single eye is, in reality, made up of many hundreds of 

 smaller facets or microscopical windows, the whole resembling in 

 every detail the exterior of a piece of honeycomb. 



Behind each of these facets is an independent eye element of a com- 

 plex nature connected with the optic nerve, so that each tiny window 

 sees that part of the external object that is directly in front of it. In 

 other words, whatever the insect sees is separated into as many parts 

 as there are facets. To begin with, then, we learn that insects prob- 

 ably see things in mosaic patterns. 



Let us now take a fresh insect and place that part of its eye bearing 

 these tiny facets, under the microscope. Through the instrument we 

 observe a honeycomb sash, in which the cuticular windows are set, 

 and which appear to be quite transparent. 



By the aid of a photomicrographic apparatus, that is to say, an 

 arrangement by which we may photograph through a microscope, we 

 now mount a minute object so delicately in front of the already 

 mounted eye, that by peering into one end of the apparatus, we may 

 actually see an external object through the eye of an insect. We are, 

 so to speak, inside the fly, looking out. 



For this object a feather from the head of a humming bird was 

 chosen. By reason of its very minute size and convenient fan-shaped 

 structure it proved ideal to illustrate the qualities of focus in the 

 insect's eye. 



In figure 64 we see the result of the first photographic experiment, 



