Z MAMMALS OF THE PACIFIC WORLD 



ones whose ancestors had pouches, comprise meat-eaters, gnaw- 

 ers, monkey-like creatures, and forms with hoof-like toes like 

 the kangaroos. 



For prompt and easy recognition it is best to dwell chiefly 

 upon those differences of shape or behavior which can be ob- 

 served easily. In the field most mammals are unfortunately 

 killed almost as soon as discovered, so it is best to emphasize 

 differences of shape, size, and color. The structure of certain 

 of the parts of mammals is frequently more distinctive and 

 easy to see than that of other parts ; the teeth and limbs no- 

 tably provide definite indications of species, and usually agree 

 with the evidence of other parts and with fossil evidence. 



Teeth. Although the toothed whales may have as many as 

 fifty teeth on each side of each jaw, other mammals never have 

 more than that number all together. The Australian meat- 

 eating pouched animals or marsupials may have a total of 

 forty-six teeth (our opossum has four more) ; most other mam- 

 mals have far fewer — at the most forty-four. The spiny and 

 scaly anteaters have none, but lap up their insect prey with a 

 long, sticky tongue; and the whalebone whales have replaced 

 teeth with a horny set of sieves that retain engulfed small fish 

 and shrimp-like animals for swallowing. 



The teeth of mammals, except the simple, peg-like teeth of 

 the toothed whales, consist of several sorts. They comprise 

 front cutting-teeth, or incisors ; pointed, often fang-like eye- 

 teeth, or canines; narrowed cheek-teeth in the side of the jaw 

 near the front, or premolars ; and broader crushing-teeth near 

 the back, or molars. In some kinds of animals the teeth of one 

 class may assume the shape and function of another class. In 

 many mammals all but the molars develop in two successive 

 series, a milk or juvenal series, and a permanent or adult series 

 which replaces the former. In pouched animals one tooth only 

 in each jaw is so replaced. The toothed whales have only 

 permanent teeth. Squirrels and porcupines among the gnawing 

 mammals replace one or two cheek-teeth at about the time they 



