INTRODUCTION 
DEFINITION OF COMMON BIOLOGICAL TERMS 
Adaptation. — Have you ever seen a squirrel run up a tree, 
hurry along the branches, then jump to another tree and 
disappear in the foliage? 
Did it occur to you as 
you watched him that he 
was adapted to the mode 
of life that he 'was lead¬ 
ing? His toes are pro¬ 
vided with sharp, curved 
nails that make it easy 
for him to hold fast to 
the rough bark of the 
tree ; and, when he jumps 
from branch to branch, 
his tail acts as a para¬ 
chute, so that his front 
feet alight first. 
Did you ever notice 
how he holds the nut in 
his front feet and how he 
uses his cutting teeth to 
get the kernel ? The feet 
thus used as hands and 
the teeth used for cutting 
are adaptive features. If 
a squirrel has more food 
than he can eat at once, 
he takes the nuts and buries them in the earth. In doing 
this he uses his front feet for digging a hole in the ground 
Figure 1. 
Notice how the squirrel holds the nut 
with his front feet. What use is made of 
his hind feet at this time ? Are his front 
feet being used as hands or feet ? Com¬ 
pare the tail of the squirrel with the tail of 
a mouse (Figure 120). Of what use to a 
squirrel is a big bushy tail ? Would such 
a tail be useful to a mouse ? Would it be 
a detriment ? Why ? 
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