320 BRANCH CHORDATA 



at night for food. An allied form, the nodiak, is eaten by the aborigines 

 of the Papuan region. 



The duck-bill (Ornithoryri chus) (Fig. 262) is found in southern and 

 eastern Australia and Tasmania. It has a small, round head, and a 

 broad, flattened, sensitive bill. Its eyes are small and somewhat hidden, 

 but well developed. Its great paddling feet are five toed and webbed, the 

 webs of the anterior feet being longer than the claws. It is about the size of 

 our common rabbit and has short legs and a flattened tail. Its body is 

 covered with loose skin, protected by thick, glossy hair, with an under layer 

 of fine waterproof fur. The duck-bill is aquatic, digging burrows 30 or 40 

 feet long in the banks of streams. One opening of this burrow is below the 

 water. It dives, enters this opening, and is safe from its enemies. It has 

 teeth when young, but soon sheds them, and the gums harden into horny 

 plates for crushing insects, worms, snails, and mussels, which it digs out of 

 the mud with its snout and stores away in its cheek pouches to be eaten as 



Fig. 262. Duck-bill (Ornithorhynchus paradoxus). (From Liitken.) 



it drifts upon the water. Sight and hearing are acute, but it has no external 

 ears. The male is armed with a strong horny spur on each hind foot, 

 which is connected with a poison gland. The duck-bill is as shy as a beaver. 

 Its voice is like the growl of a puppy. The young are blind and naked. 



Order II. Marsupia'lia. Marsupials are fur-covered, terres- 

 trial (rarely aquatic), or arboreal, or subterranean mammals, 

 which carry the young, born immature, naked, and blind, at- 

 tached to the mammary gland in an abdominal integumentary 

 pouch. The milk is forced down the throat of the young by 

 the muscular action of the mother. The young are able to 

 breathe at the same time by the wrapping of the soft palate 

 around the upper end of the trachea in such a manner that the 

 air may pass from the nose down the trachea while the milk 

 passes down the throat. The clavicle is present. The cloaca 



