In my specimen, just after death the patches were quite oily, the substance coming off upon the hands, and smelling like ordinary bird oil. As soon as possible I took the bird into a perfectly dark room, to test it for phosphorescent light, but not the slightest gleam was perceptible. Just under the patches a large accumulation of fat is seen; and from these portions probably exudes the substance, which, during the life of the bird, becomes luminous upon exposure to the air. In the specimen alluded to, after it had been dead for several days, the shafts of the feathers of the patch seemed suffused with a dark oily substance. The feathers of the powder-down patches did not burn more readily than feathers from other parts, and the odor was the same. These patches are not strictly confined to cranes and herons. The kirumbo (or _Leptosmus discolor_) of Madagascar has a highly developed patch upon each side of the rump. These birds are related to the rollers, and are remarkable for their games in mid-air. The bitterns have two pairs of powder-down patches, the true herons three, and the curious boatbills (_Cochlearius_) four pairs, which, if all luminous, must render them the centre of attraction in the South-American swamps. The interesting oil-bird _Podargus_ (or Guarcharo), that builds in the island of Trinidad and on various parts of the South-American coast, is a fruit-eating, nocturnal bird allied to the night-hawks. Curiously enough, it has no oil-glands, but two large powder-down patches, one on each side of the rump, composed, according to Dr. Sclater, who made the discovery, of about forty feathers each. In Plate XXVII., an ideal view is given of the possible appearance of the light of a large heron (_Ardeomega goliath_) of Africa. Whether these lights are of sufficient brightness to attract fishes is a question; but, knowing that fishes are readily attracted by light of fire, we may well imagine that a crane or heron, if standing in the water in perfect stillness, with this soft light a short distance above it, might possibly avail itself of such a lure, though such a view is purely conjectural. Mr. Charles Harris of Pasadena, Cal., informed me that several years ago he entered a heronry in Maine on a dark night, and distinctly observed numbers of lights too large for insects; and, moreover, they disappeared with the birds, so that he was impressed that there was some association between the light and the herons.