General Phenomena of Colour in the Organic World--Theory of Heat and Light as producing Colour--Changes of Colour in Animals produced by Coloured Light--Classification of Organic Colours--Protective Colour--Warning Colours--Sexual Colours--Typical Colours--The Nature of Colour--Colour a normal product of Organization--Theory of Protective Colours--Theory of Warning Colours--Theory of Sexual Colours--Colour as a means of Recognition--Colour proportionate to Integumentary Development--Selection by Females not a cause of Colour--Probable use of the Horns of Beetles--Cause of the greater brilliancy of some Female Insects--Theory of display of Ornaments by Males--Natural Selection as neutralizing Sexual Selection--Theory of Typical Colours--Colour-development as illustrated by Humming-birds--Local causes of Colour-development--Summary on Colour-development in Animals. There is probably no one quality of natural objects from which we derive so much pure and intellectual enjoyment as from their colours. The heavenly blue of the firmament, the glowing tints of sunset, the exquisite purity of the snowy mountains, and the endless shades of green presented by the verdure-clad surface of the earth, are a never-failing source of pleasure to all who enjoy the inestimable gift of sight. Yet these constitute, as it were, but the frame and background of a marvellous and ever-changing picture. In contrast with these broad and soothing tints, we have presented to us in the vegetable and animal worlds, an infinite variety of objects adorned with the most beautiful and most varied hues. Flowers, insects and birds, are the organisms most generally ornamented in this way; and their symmetry of form, their variety of structure, and the lavish abundance with which they clothe and enliven the earth, cause them to be objects of universal admiration. The relation of this wealth of colour to our mental and moral nature is indisputable. The child and the savage alike admire the gay tints of flower, bird, and insect; while to many of us their contemplation brings a solace and enjoyment which is both intellectually, and morally beneficial. It can then hardly excite surprise that this relation was long thought to afford a sufficient explanation of the phenomena of colour in nature; and although the fact that-- “Full many a flower is born to blush unseen, And waste its sweetness on the desert air--”