Now let us discuss the visual acuity we could expect from the bee. The eye of a bee is a compound eye, and it is made of a large number of special cells called ommatidia, which are arranged conically on the surface of a sphere(roughly)on the outside of the bee's head. Figure 36-7 shows a picture of one such ommatidium At the top there is a transparent area, a kind of"lens, "but actually it is more like filter or light pipe to make the light come down along the narrow fiber, which is where the absorption presumably occurs. Out of the other end of it comes the nerve fiber. The central fiber is surrounded on its sides by six cells which, in fact have secreted the fiber. That is enough description for our purposes; the point is it is a conical thing and many can fit next to each other all over the surface of Jow let us discuss the resolution of the eye of the bee. If we draw lines(Fig 36-8)to represent the ommatidia on the surface, which we suppose is a sphere of radius r, we may actually calculate how wide each ommatidium is by using our br that evolution is as clever as we are! If we have a very lar ommatidium we do not have much resolution. That is, one cell gets a piece of information from one direction, and the adjacent cell gets a piece of information from another direction, and so on, and the bee cannot see things in between very well.So the uncertainty of visual acuity in the eye will surely correspond to an angle, the angle of the end of the ommatidium relative to the center of curvature of the eye. (The eye cells, of course, exist only at the surface of the sphere; inside Fig. 36-7. The structure of an om. that is the head of the bee. )This angle, from one ommatidium to the next, is, of matidium (a single cell of a compound course, the diameter of the ommatidia divided by the radius of the eye surface (36.1) So, we may " The finer we make the 8, the more the visual doesn't the bee just use very, very fine ommatidia? " Answer: We know physics to realize that if we are trying to get light down into a cannot see accurately in a given direction because of the diffraction effect. The ight that comes from several directions can enter and, due to diffraction, we will light coming in at angle Fig. 36-8. Schematic view of pack Now we see that if we make the 8 too small, then each ommatidium does not ng of ommatidia in the eye of a bee look in only one direction, because of diffraction! If we make them too big, each one sees in a definite direction, but there are not enough of them to get a good view of the scene. So we adjust the distance d in order to make minimal the total effect of these two. If we add the two together, and find the place where the sum has a minimum(Fig. 36-9), we find that d(△n+△a (36.3) d8 △·/8 which gives us a distance Fig. 36-9. The optimum size for an If we guess that r is about 3 millimeters, take the light that the bee sees as 4000 (3×10-3×4×10-7) The book says the diameter is 30u, so that is rather good agreement! So, apparently, it really works, and we can understand what determines the size of the bee's ey It is also easy to put the above number back in and find out how good the bee's eye actually is in angular resolution; it is very poor relative to our own. We can things that are thirty times smaller in apparent size than the bee; the bee has a rather fuzzy out-of-focus image relative to what we e. Nevertheless it is all right, and it is the best they can do. We might ask why the bees do not develop