712 MAMMALIA. 



harmony between their colouring and that of their surround- 

 ings ; thus the white Arctic fox and hare are inconspicuous 

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

 many tawny animals harmonise with the sandy background 

 of the de'sert. 



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 ; 

 sentinels are posted and social conventions are respected ; 

 such migrations as those of the lemming and reindeer are 

 characteristically social. In the beaver village and among 

 monkeys there is combination in work, and their communal 

 life seems prophetic of that sociality which is distinctively 

 human. 



Among Birds, mates are won by beauty of song and 

 plumage ; Mammals not less characteristically woo by force. 

 Rival males fight with one another, and are usually larger 

 and stronger than their mates. The antlers of male deer, 

 the tusk of the male narwhal, the large canine teeth of boars, 

 illustrate secondary sexual characters useful as weapons. 

 But manes and beards, bright colours and odoriferous 

 glands, are often more developed in the males than in 

 the females, and may be of advantage in the rough 

 mammalian courtship. At the breeding season a remark- 

 able organic reaction often affects the animal : the timid 

 hare becomes a fierce combatant, and love is often 

 stronger than hunger. The courtship of Mammals is 

 usually like a storm violent but passing ; for, after pair- 

 ing, the males return to their ordinary life and the 

 females become maternal. Some monkeys are faithfully 

 monogamous ; and exceptional pairs, such as beavers and 

 some antelopes, remain constant year after year; but this is 

 not the way of the majority. 



The duckmole lays eggs and brings up her young in the 

 shelter of the burrow ; the Echidna has a temporary pouch. 

 In Marsupials the time of gestation is very short, and there 

 is rarely a true placental union between the unborn young 

 and the mother. The new-born Marsupials are very helpless, 

 and are in most cases transferred to an external pouch or 

 marsupium, within which they are nurtured. In Eutherian 



