1 86 EXTINCT MONSTERS. 



afterwards impressed by the hind feet, so that each track contains 

 two impressions. 



The reader who has some knowledge of natural history will not 

 need to be told that the sloths of the present day, inhabiting the 

 same region as their gigantic ancestors, are of small size, and live 

 among the branches of the trees, together with the spider monkeys, 

 howlers, and other apes. An interesting question to the evolutionist 

 is — How did the change take place from the old huge and heavy 

 types to the smaller and agile types of the present day ? Can it be 

 possible that the more difficult and tedious task of pulling down 

 branches and even stems of trees, in order to devour the leaves, was 

 abandoned for the simpler method of climbing up and feeding 

 among the branches ? It certainly looks as if a change of this kind 

 had been instituted at some distant period in the past — distant, 

 that is, to us, but not very remote geologically. The present 

 method seems so much simpler that we need not be surprised at its 

 adoption, for Nature is ever ready to encourage and assist those 

 among the children of Life which can hit upon and adopt new 

 and improved methods, either in obtaining food or repelling 

 enemies, or other duties imposed upon them. Now, suppose 

 that, in accordance with the well-known fact that variations in 

 the offspring of animals are constantly cropping up, some con- 

 siderably smaller variety of Megatherium, or Mylodon, or other 

 now extinct type, appeared on the scene, and, by virtue of its 

 comparative agility, could climb a tree and feed among the 

 branches instead of pulling them down : then, as Darwin has so 

 well explained, Nature would seize upon this accidental variation, 

 and give it an advantage over its more awkward relations. Its 

 offspring, too, would inherit the same characteristics, they would 

 adopt the same habits, and, in time, as " natural selection " further 

 increased these characters, by weeding out those that were unfit 

 while fostering all those that were neither large nor clumsy in 

 climbing trees, a new race of sloths would arise. This new race, 

 it can well be imagined, would in time outstrip the old race in 



