530 MAMMALS. 



phalangers," such as Fetaurus, among Marsupials ; " flying- 

 squirrels," such as Pteromys, among Rodents ; " flying- 

 lemurs " {Galeopithecus), allied to Insectivores. Not a few 

 are aquatic, — all the Cetaceans, the two Sirenians, and the 

 Pinniped Carnivores, such as seals and walruses ; while 

 water-voles, beavers, otters, polar bear, and many others are 

 also at home in the water. Burrowers are well-represented 

 by moles and rabbits; arboreal forms by squirrels and 

 monkeys. 



As to diet, man, most monkeys, pigs, and many others, 

 may be called omnivorous ; kangaroos, hoofed animals, and 

 most rodents are herbivorous ; the echidna, the ant-eaters, 

 hedgehogs and shrews, and some bats are insectivorous; 

 most of the Carnivora are carnivorous ; dolphins and seals 

 feed chiefly on fishes ; but in most cases the diet varies not 

 a little with the available food-supply. 



The struggle for existence among Mammals is sometimes 

 keen among fellows of the same kind ; thus the brown rat 

 {Mus decumanus) tends to drive away the black rat {M. 

 rattus), but stress, due to over-population, is sometimes 

 mitigated by migration, as in the case of the lemmings. The 

 struggle seems to be keener between foes of different kinds, 

 between carnivores and herbivores, between birds of prey 

 and small mammals; but combination for mutual defence 

 often mitigates the intensity of the conflict. Teeth and 

 claws, hoofs and horns are the chief weapons, while the 

 scales of pangolins, the bony shields of armadillos, the spines 

 of hedgehogs and porcupines, and the thick hide of the 

 rhinoceros may be regarded as protective armature. In 

 keeping their foothold some mammals are helped by the 

 harmony between their colouring and that of their surround- 

 ings ; thus, the white Arctic fox and hare are inconspicuous 

 on Hhe snow, the striped tiger is hidden in the jungle, 

 and many tawny animals harmonise with the sandy back- 

 ground of the desert. 



The majority of Mammals are gregarious, witness the herds 

 of herbivores, the cities of the prairie-dogs, the packs of 

 wolves, the schools of porpoises, the bands of monkeys. 

 Combinations for attack and for defence are common ; senti- 

 nels are posted and social conventions are respected ; such 

 migrations as those of the lemming and reindeer are char- 



