XX 
GROWING, BREATHING, AND OTHER THINGS 
PINNERS grow, of course, but 
they do not grow a little every 
day as kittens and birds do. 
Instead they grow by starts and 
spurts. There is a good reason for 
this. The outside covering of their 
bodies is hard and tough. It is the 
hardest part of their bodies, for it is 
really all the skeleton that they have. 
Now this skeleton does not grow, and 
it is too hard to stretch ; so when the 
Spinner has grown as big as it can 
inside this covering, there is nothing 
to do but cast it off and get a new 
one. 
That is just what is done. The 
babies are only a few days old when 
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