186 LEXTINCT MONSTLES: 
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? Canit 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 ws, 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 
