Among mammals, all of which belong to the vertebrates, mimicry is seldom found, and it is supposed that only one genuine case has been observed. Cladobates, an insect-eating genus found in the Malayan region, includes many species closely resembling squirrels both in size and color, as well in regard to the bushiness and position of the tail. It is supposed by Mr. Wallace that Cladobates, owing to its resemblance to the harmless fruit-eating squirrel, may be enabled to approach insects and birds upon which it lives. Cuckoos bear a considerable resemblance to hawks; the cuckoo tribe being weak and defenceless will in this way be enabled to elude the voracious hawks. There is a genus of dull-colored birds in Australia and the Moluccas named Tropidorhynchus. These birds are large, active, and strong, with powerful claws and sharp beaks. They congregate in flocks, and are remarkably aggressive, driving away crows and even hawks. In these same countries a genus of the group orioles lives, named Mimeta. These are much weaker than their allies the golden orioles, and besides are devoid of their brilliant colors, being usually olive-green or brown. It is a very common thing to find species of the Mimeta resembling Tropidorhynchi living on the same island. The Tropidorhynchus bouruensis and Mimeta bouruensis are both found in the island of Bouru, the latter of which mimics the former as described by Mr. Wallace: “The upper and under surfaces of the two birds are exactly of the same tints of dark and light brown. The Tropidorhynchus has a large, bare, black patch round the eyes; this is copied in the Mimeta by a patch of black feathers. The top of the head of the Tropidorhynchus has a scaly appearance from the narrow scaly-formed feathers, which are imitated by the broader feathers of the Mimeta, having a dusky line down each. The Tropidorhynchus has a pale ruff, formed of curious recurved feathers on the nape (which has given the whole genus the name of friar birds); this is represented in the Mimeta by a pale band in the same position. Lastly, the bill of the Tropidorhynchus is raised into a protuberant keel at the base, and that of the Mimeta has the same character, although it is not a common one in the genus.” The result is that when superficially examined the birds seem to be identical, though possessed of important structural differences, and placed wide apart in any natural arrangement. Mr. Wallace mentions some curious cases of mimicry among reptiles, where a venomous tropical genus of snakes, Elaps, belonging to America, is closely mimicked by several genera of harmless snakes. It is in a special degree among insects that cases of mimicry are most frequently found.