are at home in the tree tops; and squirrels, opossums, coons, bears, cats, monkeys, apes, and sometimes man, find up among the branches of a tree the situation that meets pleasure or necessity.
Launching out into the air, the most difficult path to take, most hazardous and most perilous, but attempted by many different kinds of animals, is another highway. Some faint suggestion of an effort to utilize the air in locomotion is shown by the wind-blown Portuguese man-of-war, and more fully by the aeronautic spider who launches his balloon of silk for aerial flight, but no real success as traveler of the air is found until we reach the group of insects, where wings—true aerial organs of locomotion—become a conspicuous characteristic of the group. How well they have succeeded is testified by the fact that such locomotion has been in vogue with them since early paleozoic time, and, considering their size, the speed and endurance exhibited in air is equaled by no other kind of animal.
The flying-fish, driven from its native element by pursuing foe to temporary elevation in the air, is a strange abortive attempt to reach this goal, but it has taken too direct a course ever to succeed. It should have first become an air-breathing land animal before attempting the soaring act. The frogs and lizards with expanded feet for floating on the air are poor apologies for flying animals, but given time might reach that goal were not the field so fully occupied by more dominant forms. The ancient flying reptiles, known only by their fossils, reached a high degree of efficiency, if we may judge by the expanse of wing they show. In their time they were doubtless the dominant types of the air, but they left no legacy to later forms, for the wings of modern groups are formed on different plans and must have been developed de novo or regardless of the reptilian type.
So now we reach the birds—the truest, most perfect of aerial forms, the animals which, with natural organs, have come nearest to annihilating time and space—whose skill in traversing the trackless regions of aerial waste has been the constant envy of man, from early time down to Darius Green, Maxim and Langley and a host of modern inventors. 'O had I wings' in various refrains has been the lament of man till we may expect ere long that the want will be practically supplied. Some birds indeed do not seem to appreciate this gift and have sacrificed these organs to adapt themselves to water or to a speedy gait on land, but flight is the dominant mode of locomotion for the group. Some of the mammals, aside from man, have attempted to follow the lead of the birds and the bats have succeeded so well that they are practically cut off from all other modes of locomotion, while flying phalangers, flying squirrels, and others attest the effort in various groups to adopt this rapid though hazardous kind of locomotion.
