338 THE POPULAR SCIENCE MONTHLY, 



very class of insects, bees, as Sir John Lubbock's experiments show 

 us, do undoubtedly distinguish between red, orange, yellow, and green. 

 Butterflies also are attracted by colors, and will, in particular, fly down 

 to objects of the same hue as their own mates. Of course, bees and 

 butterflies, always living among flowers, especially require a good 

 sense of color ; and so they quite accord with our expectation. Wasps, 

 again, are omnivorous creatures, living partly upon animal and partly 

 upon vegetable food. Everybody knows that they will quite impar- 

 tially feast upon a piece of raw meat or upon the sunny side of a 

 peach. Now, wasps, as Sir John Lubbock proved, can also distinguish 

 colors ; but they are somewhat less guided by them, apparently, than 

 are bees ; and this again bears out the same generalization. Ants are 

 much more miscellaneous in their diet, they have no wings (roughly 

 speaking), and they do not visit flowers except by the casual process 

 of walking up the stems. Hence a color-sense would be of little or 

 no use to them : and Sir John Lubbock's experiments seem to show 

 that they scarcely possess one, or only possess it in a rudimentary 

 form. Once more, moths fly about in the dusk, or quite at night, and 

 the flowers which lay themselves out to attract them are white or pale 

 yellow, since no others are visible in the evening. Thus a perception 

 of red, blue, or orange would probably be useless to them : and Mr. 

 Lowne has shown that the eyes of nocturnal insects differ from those 

 of diurnal insects in a way closely analogous to that in which the eyes 

 of bats and owls differ from those of monkeys and humming-birds. 

 These differences are probably connected in both cases with an absence 

 of special organs for discriminating colors ; and we shall see a little 

 later on that, while the day-flying butterflies are decked in crimson 

 and orange to please the eyes of their fastidious mates, the night-flying 

 moths are mostly dull and dingy in hue, or reflect the light only in 

 the same manner as the night-flowering blossoms among which they 

 seek their food. Ascending to the vertebrates, the birds are the class 

 which live most in a world of fruits or flowers ; and Mr. A. R. Wal- 

 lace has pointed out that birds on the whole need to perceive color 

 more than any other animals, because their habits require that they 

 should recognize their food at a considerable distance. But birds pos- 

 sess a very large proportion of certain nerve-terminals called the cones, 

 which are three times as numerous in their eyes as the other kind, 

 called rods. These cones are almost universally believed to be the 

 special organs of color-perception, and in mammals they are actually 

 less numerous than the rods, which are supposed to be merely cogni- 

 zant of light and shade. Nocturnal birds, such as owls, have very 

 few cones, while nocturnal mammals have none. Again, the yellow 

 spot in the retina, consisting almost entirely of cones, is found in all 

 diurnal birds ; but among mammals it occurs only in the fruit-eating 

 class of monkeys, and in man. So that on the whole we may say the 

 positive evidence justifies us in believing that a highly-developed 



