It is noteworthy that these bright markings on the upper surface are, usually, not visible when the bird is at rest. The white wing patch folds in, the white rump is covered, while, in a white-tipped tail, it is usual for the two centre feathers to be plain throughout (see illustrations of species 313 and 329). The tail is folded, and the white tips are covered by the two non-white centre feathers. The introduced Indian Turtle-Dove, common about nearly every city in Australia, shows the spread-out, white-tipped tail splendidly when flying. The bird itself is barely visible if it settles in the shade or on the soil. The Indian Myna, a city bird, has both white wing-patch and white-tipped tail. This explanation is also applied to other wild animals; thus many Deer have the white patch on the hind quarters. Other Deer, seeing this warning signal displayed in flight, immediately make for safety. Similarly, Wallace has explained the white tail of a Rabbit. The Skunk also has this white patch on the hind quarters, but here a different explanation is required, for the Skunk does not trouble to run away when a possible enemy appears. The bright color is here regarded as an "advertizing color." The Skunk has other means of protection, and he is labelled dangerous or objectionable, just as our one poisonous Spider is plainly labelled dangerous by means of a red stripe. An inexperienced enemy may rush at the Skunk, but the means of protection enjoyed by it effectively protects it, and the enemy retires. It is a rule recognized by collectors that conspicuous animals have generally some effective means of protection, and they are best left alone, or at least taken with caution. This is readily understood when it is considered that a young, inexperienced chicken will rush at a brightly-colored caterpillar. He then retires, endeavoring to get rid of the objectionable taste. For the future, he avoids brightly-colored animals. Thus the bright color is an obvious advantage to its possessor, as it saves a dangerous peck. It is also an advantage to its enemies, for it saves them an unpleasant experience. We are told the Parrot is the only bird with a sense of taste, but it seems that the chicken possesses one also. Still another phase of color is shown by Diamond-Birds, where three species have a yellow spot, a red spot, or an orange spot respectively on the wing. It is also shown by the Red-breasted Robins. One has a white forehead, one a white cap, and the third a red cap. These colored patches are considered to be recognition marks, so that a bird can recognize its mate, or a bird of its own kind, readily and with certainty.