a good eye like our own, with a lens and so on. There are several interesting rea sons. In the first place, the bee is too small; if it had an eye like ours, but on his scale, the opening would be about 30 u in size and diffraction would be so impor tant that it would not be able to see very well anyway. The eye is not good if it is too small. Secondly, if it were as big as the bee's head, then the eye would occupy the whole head of the bee. The beauty of the compound eye is that it takes up no space, it is just a very thin layer on the surface of the bee. So when we argue that they should have done it our way, we must remember that they had their own 36-5 Other eyes Besides the bees, many other animals can see color. Fish, butterflies, birds, and reptiles can see color, but it is believed that most mammals cannot. The primates can see color. The birds certainly see color, and that accounts for the colors of birds. There would be no point in having such brilliantly colored males if the females could not notice it! That is, the evolution of the sexual"whatever it is"that the birds have is a result of the female being able to see color. So next time we look at a peacock and think of what a brilliant display of gorgeous color it is and how delicate all the colors are and what a wonderful aesthetic sense it takes to appreciate all that, we should not compliment the peacock, but should compliment the visual acuity and aesthetic sense of the peahen, because that is what has generated the beautiful scene! All invertebrates have poorly developed eyes or compound eyes, but all the vertebrates have eyes very similar to our own, with one exception. If we consider the highest form of animal, we usually say, " Here we are!, but if we take a less prejudiced point of view and restrict ourselves to the invertebrates, so that we cannot include ourselves, and ask what is the highest invertebrate animal, most zoologists agree that the octopus is the highest animal! It is very interesting that, besides the development of its brain and its reactions and so on, which are rather good for an invertebrate, it has also developed, independently, a different eye. is not a compound eye or an eye spot-it has a cornea, it has lids, it has an iris, it has a lens, it has two regions of water, it has a retina behind. It is essentially the same as the eye of the vertebrates! It is a remarkable example of a coincidence in olution where nature has twice discovered the same solution to a problem, with one slight improvement. In the octopus it also turns out, amazingly, that the retina is a piece of the brain that has come out in the same way in its embryonic develop ment as is true for vertebrates but the interesting thing which is different is that the cells which are sensitive to light are on the inside, and the cells which do the cal culation are in back of them, rather than"inside out, "as in our eye. So we see, at least, that there is no good reason for its being inside out. The other time nature tried it, she got it straightened out!(See Fig 36-10. The biggest eyes in the world Fig. 36-10. The eye of an octopus are those of the giant squid; they have been found up to 15 inches in diameter 36-6 Neurology of vision One of the main points of our subject is the interconnection of information from one part of the eye to the other Let us consider the compound eye of the horseshoe crab, on which considerable experimentation has been done. First of all, we must appreciate what kind of information can come along nerves. A nerve carries a kind of disturbance which has an electrical effect that is easy to detect,a kind of wavelike disturbance which runs down the nerve and produces an effect at the other end: a long piece of the nerve cell, called the axon, carries the infor mation along, and a certain kind of impulse, called a"spike, " goes along if it is excited at one end. When one spike goes down the nerve, another cannot immedi- ately follow. All the spikes are of the same size, so it is not that we get higher pikes when the thing is more strongly excited, but that we get more spikes per second. The size of the spike is determined by the fiber. It is important to appreci ate this in order to see what happens next