A remarkable bird of South America, the bell-bird, has a peculiar note that “can be distinguished at the distance of nearly three miles and astonishes every one who hears it.... The male is pure white, whilst the female is dusky-green; and white is a very rare color in terrestrial species of moderate size and inoffensive habits. The male, also, as described by Waterton, has a spiral tube, nearly three inches in length, which rises from the base of the beak. It is jet-black, dotted over with minute downy feathers. This tube can be inflated with air, through a communication with the palate; and when not inflated hangs down on one side. The genus consists of four species, the males of which are very distinct, whilst the females, as described by Mr. Sclater in a very interesting paper, closely resemble each other, thus offering an excellent instance of the common rule that within the same group the males differ much more from each other than do the females. In a second species (_C. nudicollis_) the male is likewise snow-white, with the exception of a large space of naked skin on the throat and round the eyes, which during the breeding season is of a fine green color. In a third species (_C. tricarunculatus_) the head and neck alone of the male are white, the rest of the body being chestnut-brown, and the male of this species is provided with three filamentous projections half as long as the body—one rising from the base of the beak, and the two others from the corners of the mouth.” The most familiar case of sexual difference amongst North American birds is that of the scarlet tanager, in which the male is scarlet with jet-black wings, while the female is an inconspicuous yellow-green color. Amongst domesticated animals the peafowl shows the most beautiful case of sexual differences. The magnificent tail of the male can be lifted up, so as to be seen to best advantage when the male faces the observer. Moreover the wild form, living in the forests of India, has the same gorgeous train. The male Argus pheasant has a remarkable series of spots, or ocelli, on the secondary wing-covers. They are concealed until the male displays them before the female. Darwin states that, while it may seem incredible that such elegant shading and exquisite patterns could have been the outcome of the taste of the female, yet the extraordinary attitude assumed by the male during courtship appears entirely purposeless, unless it be supposed that he is attempting to charm the female by a display of his ornamentation.