Natural History 495 



As far as the eye can embrace the prairie, it sees heaps of 

 earth, and on each of them a prairie-dog stands, engaged in a 

 lively conversation with its neighbours by means of short 

 barkings. As soon as the approach of man is signalled, all 

 plunge in a moment into their dwellings ; all have disappeared 

 as by enchantment. But if the danger is over, the little crea- 

 tures soon reappear. Whole families come out of their 

 galleries and indulge in play. The young ones scratch one 

 another, they worry one another, and display their graceful- 

 ness while standing upright, and in the meantime the old ones 

 keep watch. They go calling on one another, and the beaten 

 footpaths which connect all their heaps testify to the fre- 

 quency of their visits. 



As Darwin said, "the individuals which took the greatest 

 pleasure in society would best escape various dangers ; while those 

 that cared least for their comrades and lived solitary, would perish 

 in great numbers." In short, the line of mutual aid is a trend of 

 evolution, which has borne its finest fruits in mankind. 



17 

 Variety among Mammals 



We see the March hares racing over the ploughed field, and 

 the sloths creeping cautiously along the under side of the branches. 

 The porpoises gambol in the sea, and the bats with erratic flight 

 hawk insects in the air. The mole works its way for the most part 

 underground, and the squirrel leaps adventurously from tree to 

 tree. Whales are mammals of the open sea, and sometimes 

 descend to great depths ; monkeys are largely arboreal ; antelopes 

 are suited for the plains and the hippopotamus for the rivers. 

 Wild cattle are gregarious, beavers are social, the sea-lion has his 

 harem, the polar bear is solitary. We watch seals resting among 

 the shore rocks, and bats hanging upside down from the rafters. 

 In the winter the wolves join in packs, the stoat turns into the 

 white ermine, the hedgehog sinks into hibernation. There are 

 herbivores, insectivores, carnivores, specialists like the ant-eaters 



