386 A HISTORY OF BIRDS 



feathers are traceable ; moreover, no flexion of the fore-arm or 

 manus is possible — that is to say, the wing cannot be closed, 

 as in wings which serve the purposes of flight. The skeleton of 

 this wing, in the adult, reveals a great flattening and broadening, 

 and a curious enlargement of the carpals. But in the embryo 

 a distinct pollex is traceable, and the whole limb agrees closely 

 with that of a typical wing, capable of flight. 



The shoulder girdle displays no very remarkable features, 

 save an enormously broad scapula ; while the hind-limb, it is 

 to be noticed, has the toes webbed and the girdle of the elon- 

 gated type; as if originally the work of propelling the body 

 fell upon the pelvic limb, as in the cases already considered. 

 And it is significant to note that among the Auks to-day the 

 wings are often used to accelerate progress under water. In 

 the ancestral Penguins it would seem this auxiliary became 

 finally the sole means of locomotion. 



The extreme modification of the limbs and girdle, it is to 

 be noticed, only occur in those types which obtain all their food 

 beneath the surface of the water. The Coots and Water-hens, 

 which swim well but pass much of their time and obtain much 

 of their food on land, have undergone but little change in the 

 direction of adaptation to swimming ; it would seem indeed 

 that these birds, before they adopted their present aquatic 

 habitat, had sojourned long in an environment where cursorial 

 powers of no low order were essential to existence. And this 

 because the pelvis bears evident signs of specialisation de- 

 signed to effect this end. To this fact we shall refer at the 

 proper time. Certain near allies of these birds indeed, such as 

 the Corn-crake, live far from water, skulking amid dense 

 undergrowth in the driest regions. 



It is generally supposed that webbed feet are essential to 

 birds which swim ; this, however, is not the case. The Coots 

 and Water-hens, for example, are expert swimmers and divers 

 yet the toes are free. In the former the toes are, however, 

 provided with broad lobes of integument on either side ; in the 

 latter they are not so furnished, but are of great length and 

 slenderness. The Gulls, near allies of the Plovers — which have 

 free toes — have webbed feet, though they do not swim so much, 

 nor depend so much on swimming for their livelihood as those 

 members of the Rail tribe, the Coots and Water-hens. The 



