) 



126 ANIMAL LOCOMOTION. . 



and extensive surfaces, — weight in either case being a sine 

 qua non. In order to utilize the air as a means of transit, 

 the body in motion, whether it moves in virtue of the life it 

 possesses, or because of a force superadded, must be heavier 



Fig. 59. — The Red-legged Partridge (Perdix rubra) with wings fully extended 

 as in rapid flight, shows deeply coneave form of the wings, how the primary 

 and secondary feathers overlap and support each other during extension, 

 and how the anterior or thick margins of the wings are dii'ected upwards 

 and forwards, and the posterior or thin ones downwards and backwards. 

 The wings in the partri<tge are wielded with iiijiiiense velocity and power. 

 This is necessary because of their small size as compared with the great 

 dimensions and weight of the body. 



If a horizontal line be drawn across the feet {a, e) to represent the horizon, 

 and another from the tip of the tail («) to the root of the wing (d), the angle 

 at which the wing strikes the air is given. The body and wings Avhen taken 

 together form a kite. The wings in the partridge are rounded and broad. 

 Compare with heron, fig. 60. — Original. 



than the air. It must tread and rise upon the air as a swim- 

 mer upon the water, or as a kite upon the wind. It must 

 act against gravity, and elevate and carry itself forward at 

 the expense of the air, and by virtue of the force which 



Fig. 60 — The Grey Heron (Ardea cinerea) in full flight. In the heron the 

 wings are deeply concave, and unusually large as compared with the size of 

 the bird. The result is that the wings are moved very leisurely, with a slow, 

 heavy, and almost solemn beat. The heron figured weighed under 3 lbs. : 

 and the expanse of wing was considerably greater than that of a wild goose 

 which weighed over 9 lbs. Flight is consequently more a question of power 

 and weight than of buoyancy and surface, d, e, f Anterior thick strong 

 margin of right wing, c, a, b Posterior thin flexible margin, composed of 

 primary (b), secondary (a), and tertiary (c) feathers. Compare with part- 

 ridge, fig. 59. — Original. 



resides in it. If it were rescued from the law of gravity on 

 the one hand, and bereft of independent movement on the 

 other, it would float about uncontrolled and uncontrollable, 

 as happens in the ordinary gas-balloon 



