DIVISIONS OF BIRDS. 



475 



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. jThey 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. 



Fig. 185. 



A, Foot of Cormorant i^Phalacrocorax) ; B, Beak of the 

 Bean-goose {Afiser segetum). 



The Natatores are divided into the following four families :— 

 Fam. I. BrevipennatcB. — 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 concerned, but they are employed by the bird as fins, en- 

 abling it to swim under water with great facility, and they are 

 also used on the land as fore-legs. . The feet are webbed, and 

 the hinder toe is rudimentary or wanting. The Penguins Hve 

 gregariously in the seas of the southern hemisphere, on the 

 coasts of South Africa and South America, especially at Terra 

 del Fuego, and in the solitary islands of the South Pacific. 

 When on land the Penguins stand bolt upright, and as they 

 usually stand on the shore, in long lines, they are said to present 

 a most singular, appearance. The best-known species are the 



