254 MAY AGNES HOPKINS. 



the fore-limbs came to be used as parachutes in the aerial pas- 

 sage from one tree to another. The second of these ways may 

 have been the more probable. No modern birds use their wings 

 in the manner of legs, except the young of Opisthocotmts, but 

 employ them rather as organs of flight, as balancers or as flippers 

 (penguins). 



The different modes of locomotion are intimately connected. 

 In this study of the bearing of the relation of the size of the semi- 

 circular canals to the mode of locomotion, the following main 

 kinds of locomotion were distinguished : The cursorial, where 

 the hind limbs are employed to the greatest extent, and upon 

 the hard ground ; of such birds I have examined the ostrich and 

 roadrunner. The arboreal, where wings and feet are employed 

 about equally, as in most of the passeres. A modification of the 

 preceding is the scansorial locomotion of such birds as wood- 

 peckers. The volant, where the wings are used to the greatest 

 extent, as in all birds of long sustained flight ; those with the 

 power of soaring represent the acme of this mode of locomotion. 

 The combination of volant and nektant, that is of strong flight 

 with the power of swimming, as in the gulls and albatrosses. 

 The pygopodal, which may be swimming under water (grebes), or 

 flight under the water (penguins). The grallatorial, where the 

 birds walk upon moist or yielding ground, with an elongation or 

 partial webbing of the toes ; such birds have either a strong or 

 weak power of flight and some of them can swim to a slight 

 extent. 



In the evolution of these modes of locomotion a climbing, 

 arboreal habit was probably earliest. From this would have 

 followed divergently : (a) development of stronger flight, and 

 more aerial life ; () loss of flight and terrestrial running ; (c) 

 development of a wading habit. Swimming birds have probably 

 descended from waders and divers from swimmers. The most 

 modified birds, from the standpoint of locomotion, would be the 

 two very different groups of flightless birds, the Ratitae and the 

 Sphenisci. 



In any study of genetic relationships of birds one may find 

 some help in considering the evolution of modes of locomotion. 



