Fig. 3.—Head of Drone Bee (greatly magnified). 'Ocelli' at O.
That many recognise colours there can be no doubt, and many show preferences for certain colours. Bees show a great liking for blue, and ants for violet. White butterflies appear to prefer white flowers, and yellow butterflies yellow flowers. Orange and yellow are also attractive to bees, whilst other colours seem to have no charms for them.
Fig. 2.—Head of Worker Bee (greatly magnified).
Fig. 4.—Eye of Bibio Fly. 'Ocelli' at O (greatly magnified).
There is no doubt that some insects, however, see much more of the world than others, for the eyes of the insects and their near relations, the spiders and scorpions, are of two different kinds, and both kinds differ greatly from ours in structure. Let us take the simple eye found in the spider or scorpion, for an example, and look at it. If you catch a spider, and carefully examine the front of his head, you will notice a number of bead-like bodies of different sizes, arranged sometimes in the form of a circle, sometimes on a prominent swelling or 'tubercle,' or it may be in some other fashion, according to the kind of spider. These are the eyes. A section cut through one of these eyes and placed under the microscope would show that the surface of the eye was formed by a transparent body like a lens, and that behind this lay a complicated arrangement of rods passing gradually into the nerves of sight. Only ocelli, as these eyes are called, are found in the spider and his kind. But in true insects, like the dragon-fly, or the butterfly, we meet with eyes of another kind, in addition to ocelli. These are known as compound eyes. Where compound eyes are found, the ocelli never exceed three in number, and are arranged in the form of a triangle, and placed in the middle of the head (figs. [2], [3], and [4]).