VERTEBRATA: AVES. 6oi 



the land. In accordance with their aquatic habit of life, 

 the Natatores have a boat- shaped body, usually with a long neck. 

 The legs are short, and placed behind the centre of gravity of the 

 body, this position enabling them to act admirably as paddles, at 

 the same time that it renders the gait upon dry land more or less 

 awkward and shuffling. In all cases the toes are "webbed" or 

 united by membrane to a greater or less extent (fig. 332, A). 



Fig. 332. Natatores. A, Foot of Cormorant (Phalacrocorax) ; B, Beak of the 

 Bean-goose (A nser segetum). 



In many instances the membrane or web is stretched com- 

 pletely from toe to toe, but in others the web is divided or 

 split up between the toes, so that the toes are fringed with 

 membranous borders, but the feet are only imperfectly webbed. 

 As their aquatic mode of life exposes them to great reductions 

 of temperature, the body of the Natatorial birds is closely 

 covered with feathers, and with a thick coating of down next 

 the skin. They are, further, prevented from becoming wet in 

 the water by the great development of the coccygeal oil-gland, 

 by means of which the lustrous plumage is kept constantly 

 lubricated and waterproof. They are usually polygamous, each 

 male consorting with several females; and the young are 

 hatched in a condition not requiring any special assistance 

 from the parents, being able to swim and procure food for 

 themselves from the moment they are liberated from the egg. 

 The Natatores are divided into the following four families : 

 Fam. i. Brevipennatce. In this family of the Swimming 

 birds the wings are always short, and are sometimes useless as 

 organs of flight, the tail is very short, and the legs are placed 

 very far back, so as to render terrestrial progression very 

 difficult or awkward. The family includes the Penguins, Auks, 

 Guillemots, Divers, and Grebes. In the Penguins (Spheniscidce) 

 the wings are completely rudimentary, without quills, and 

 covered with a scaly skin. They are useless as far as flight is 



