For example, where is the link which unites the Crow to the Swallow, or the Hornbill to the Humming-bird? Nevertheless all these winged creatures, so different externally, belong to the Passerines. Some Naturalists have claimed that this family presents only negative characteristics, bringing together in an odd group all the birds that are not included among the Rapacious, the Swimming, Wading, Gallinaceous or Domestic, and Climbing Birds. The principal points in common among these birds is that the outer toe is united to the middle one, more or less. Their food consists mainly of seeds, insects and fruit. They fly gracefully and easily, and their walk consists of a succession of little leaps. They build their nests and take their rest under the thick foliage of trees, or under the eaves of buildings. In this extensive family we find most of the songsters of the woodlands. Some of them have even the gift of imitating the human voice and the cries of wild animals. Many are remarkable for their brilliant plumage, others are appreciated as delicacies for the table. Some of them are easily tamed, but none of them have been brought to a domestic state. Some Naturalists divide the Passerines into five great groups, the first based upon the structure of the feet, the other four on the formation of the bill. Others object to this classification because it is not always possible to assign a place to certain groups because of peculiarities of their beak alone. This distribution is generally followed, however, as it is easy to remember. THE PERCHING BIRDS WITH UNITED TOES. As the different members of the great Passerine or Sparrow family are nearly all Perching Birds, it is easier to give them this classification in dividing them into groups, and thus avoid the many Latin names that it is not necessary to remember. In the first group we find the Perching Birds with united toes—the outer toe being nearly as long as the middle one and fast to it. This group includes the Hornbills, the Fly-catchers, the King-fishers, the Bee-eaters, and the Motmots. THE HORNBILLS.