All vertebrates have inner ear. Chemical binding causes action potential from depolarization, open channels Sweet, sour, salty, bitter Concentrated in different areas of tongue, but bud has combination of receptors. Light causes chemical change inpigment, receptor fires, neuron stimulated. Planaria eyespots, also cnidarians. Bowl-shaped, detect light direction, intensity.
Lens concentrates light on group of photoreceptors.
Light enters, fixed lens. Concave lends focus further back Farsighted eyeball too short, light focuses behind retina. Iris regulates amount of light entering eye. Color from amount and kind of pigment present. 2 layers of muscle to contract or increase pupil size.