. Beginners zoology. Zoology. Fio. 134. — Diagram of simple eye of insect. L, lens; A'', optic nerve. sight arc bic^hly developed, and consist of two compound eyes on the side of the head and three simple eyes on the top or front of the head between the com- pound eyes. The simple eye has nerve cellSi pigments, and a lens resembling the lens in the eyes of vertebrates (Fig. 134). The compound eye (Fig. 135) has thousands of facets, usually hexagonal, on its surface, the facets being the outer ends of cones which have their inner ends directed toward the centre of the eye. It is probable that t
. Beginners zoology. Zoology. Fio. 134. — Diagram of simple eye of insect. L, lens; A'', optic nerve. sight arc bic^hly developed, and consist of two compound eyes on the side of the head and three simple eyes on the top or front of the head between the com- pound eyes. The simple eye has nerve cellSi pigments, and a lens resembling the lens in the eyes of vertebrates (Fig. 134). The compound eye (Fig. 135) has thousands of facets, usually hexagonal, on its surface, the facets being the outer ends of cones which have their inner ends directed toward the centre of the eye. It is probable that the large, or compound, eyes of insects only serve to distinguish bright objects from dark objects. The simple eyes afford dis- tinct images of objects within a few inches of the eye. In gen- eral, the sight of insects, contrary to what its complex sight organs would lead us to expect, is not at all keen. Yet an insect can fly through a forest without striking a twig or branch. Is it better for the eyes that are immovable in the head to be large or small? Which has comparatively larger eyes, an insect or a beast ? Inherited Habit, or Instinct. — Insects and other ani- mals inherit frohi their parents their particular form of body and of organs which perform the different functions. For example, they inherit a nervous system with a struc- ture similar to that of their parents, and hence with a ten- dency to repeat similar impulses and acts. Repeated acts constitute a habit, and an inherited habit is called an in-. FiG. 135.—Compound Eye OF Insect. I, hexagonal facets of crystalline cones. 6, blood vessel in optic Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Coleman, Walter M. Toronto : Macmillan
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectzoology, bookyear1921
