Light is a stimulus, more or less grateful to every living creature. Reader, have you ever wandered along the sea-shore, and explored the masses of rock left uncovered when the tide is fully out; there, adhering to the surface of the stone, in little ponds, mimic bays, may be seen scores of sea-anemonies (_actinia_.) If the sky be bright, there will they be, with their painted tentacles all expanded, animal flowerets feeling the influence of light; but let the sky change, let clouds obscure the day, and they retract their tentacles and shrink into repose. These animals have no eyes, but yet they are sentient of light. We mention these sea-anemonies merely by way of example; other eyeless, and we may say, apparently nerveless creatures evidently enjoy the influence of light, as the hydra, the medusa, and the polyps of corals. If light waken up some animals from their repose--if it rouse the cock, and bid him sound his "clarion shrill," it warns others to retire to their obscure dormitory, and slumber till twilight recalls them into activity. The moth now flits abroad, and the bat and the fern-owl are on the wing, giving chase to their insect prey. The hedgehog is all alert, searching for slugs, worms, and various creeping things, which revel in the dews of sunset. It is then, too, that the fierce prowlers of the forest issue from their lair, eager for blood; but when "the sun ariseth, they gather themselves together, and lay them down in their dens." Light is not only a stimulus to animals, in the sense above noticed; it appears to be essential to health and vigour. Of this we are the less aware, because, under ordinary circumstances, we are always subject to its influence. Men have been confined for years in dark dungeons, and have reappeared upon the stage of life, pallid, meagre, weak, and emaciated beings, like breathing corpses; confinement, bad food, ill ventilation, and mental agony, had no doubt done their work; but want of light also had part in the sad devastation of the animal frame. Look, for example, at those parts of our bodies which are usually clothed, and compare the colour of the skin with that of the hands and face; strip the arm bare--the skin is acted upon by atmospheric air, but yet how much whiter than that of the hand, delicate as that hand may be. It may be said that heat, that is, solar heat, produces the difference. Partly so, no doubt, but not altogether. The face and hands of the Esquimaux are darker than his chest; moreover, suppose a severe and extensive cut happens, and that the wound thus inflicted is bound up for weeks by adhesive plaster, what do we see on removal of the straps and bandages?--a singular whiteness of the skin, the result, as it appears to us, of the exclusion of light from the covered portion. Plants, as all must have noticed, have their leaves and flowers drawn towards the light, and become pallid when kept in dark places. Thus, for example, some flowers open only when the sky is