That no fixed relation exists between the area of the wings and the size and weight of the body, is evident on comparing the dimensions of the wings and bodies of the several orders of insects, bats, and birds. If such comparison be made, it will be found that the pinions in some instances diminish while the bodies increase, and the converse. No practical good can therefore accrue to aërostation from elaborate measurements of the wings and trunks of any flying thing; neither can any rule be laid down as to the extent of surface required for sustaining a given weight in the air. The wing area is, as a rule, considerably in excess of what is actually required for the purposes of flight. This is proved in two ways. First, by the fact that bats can carry their young without inconvenience, and birds elevate surprising quantities of fish, game, carrion, etc. I had in my possession at one time a tame barn-door owl which could lift a piece of meat a quarter of its own weight, after fasting four-and-twenty hours; and an eagle, as is well known, can carry a moderate-sized lamb with facility. The excess of wing area is proved, secondly, by the fact that a large proportion of the wings of most volant animals may be removed without destroying the power of flight. I instituted a series of experiments on the wings of the fly, dragon-fly, butterfly, sparrow, etc., with a view to determining this point in 1867. The following are the results obtained:-- _Blue-bottle Fly._--_Experiment 1._ Detached posterior or thin half of each wing in its long axis. Flight perfect. _Exp. 2._ Detached posterior _two-thirds_ of either wing in its long axis. Flight still perfect. I confess I was not prepared for this result. _Exp. 3._ Detached one-third of anterior or thick margin of either pinion obliquely. Flight imperfect. _Exp. 4._ Detached one-half of anterior or thick margin of either pinion obliquely. The power of flight completely destroyed. From experiments 3 and 4 it would seem that the anterior margin of the wing, which contains the principal nervures, and which is the most rigid portion of the pinion, cannot be mutilated with impunity. _Exp. 5._ Removed one-third from the extremity of either wing transversely, _i.e._ in the direction of the short axis of the pinion. Flight perfect. _Exp. 6._ Removed _one-half_ from either wing transversely, as in experiment 5. Flight very slightly (if at all) impaired. _Exp. 7._ Divided either pinion in the direction of its long axis into three equal parts, the anterior nervures being contained in the anterior portion. Flight perfect. _Exp. 8._ Notched two-thirds of either pinion obliquely from behind. Flight perfect. _Exp. 9._ Notched anterior third of either pinion transversely. The power of flight destroyed. Here, as in experiment 4, the mutilation of the anterior margin was followed by loss of function.