444 MANUAL OF ZOOLOGY. 



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

 or united by membrane to a greater or less extent (fig. 173, A). 

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

 Bean-goose (A riser segetum). 



The Natatores are divided by Owen 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 diffi- 

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

 Guillemots, Divers, and Grebes. In the Penguins (Sphcnisddafy 

 the wings are completely rudimentary, without quills, and cov- 

 ered with a scaly skin. They are useless, as far as flight is con- 

 cerned, but they are employed by the bird as fins, enabling it to 

 swim under water with great facility. The feet are webbed, 

 and the hinder toe is rudimentary or wanting. The Pen- 

 guins live in the seas of the southern hemisphere, on the coasts 



