these birds are found not only in the tropical forests of Brazil, but also in North America and upon the snowy summits of the Andes, and can therefore hardly be used as an instance of the exclusive restriction of brilliant colour to a tropical climate. The hues of the feathers are due to two causes. In every case where there is colour at all the feathers contain a certain amount of dye, or pigment, as it is more usually termed; this pigment may be alone responsible for the colour of the feather, or it may be only a part of the cause. If the bright blue feather from a Macaw’s wing be roughly pressed so as to injure the surface, the blue colour will disappear from the rubbed place, and will be apparently replaced by a brownish black. The reason for this is that the blue colour is the result of the actual structure of the feather, which requires the underlying black pigment for its manifestation. The crushing destroys that structure and leaves only the dark pigment. The brilliant and varying hues of the soap-bubble and of mother-of-pearl are examples of substances which owe their colour to their structure; and the hues of the bird’s feather are produced by a similar kind of structure. Finely ruled lines engraved upon the feather just below a clear and transparent outer skin are responsible for the tints of different colours. But there are many birds whose colours are entirely due to the pigments. The most interesting instance of this in many ways is an African bird, the Touraco. This bird is green for the most part, but the feathers of the wings are of a magnificent crimson. When the birds take to the wing this gorgeous colour is displayed; before, it is concealed by the overlying feathers. The colouring matter can be easily extracted from the wing, and it forms a solution of a splendid crimson as bright as the substance called cochineal, which is the product of an insect. It was once said that this colour could be, and was as a matter of fact, washed out from the wings of the bird during heavy storms of rain, and that when a touraco was shot and fell into the water it stained the water red, not with its blood, but with the dye from its feathers. This is, however, an exaggerated way of putting the fact that even very feebly alkaline water will dissolve out the colour. Some of the yellows of the woodpeckers and the browns and reds of other birds are solely brought about by the presence of pigments.