By this time Peter's eyes looked as if they would pop right out of
his head. "This is the first time I've ever heard of some of those
families," said he. "My, what a lot we have to learn! Is it
because all the members of all those families have teeth for gnawing
that they are all sort of related?"

Old Mother Nature looked pleased. "Peter," said she, "I think you
ought to go to the head of the class. That is just why. All the
members of all the families I have named belong to the same order,
the order of Rodents. All the members have big, cutting, front
teeth. Animals without such teeth cannot gnaw. Now, as you and
Jumper have learned about your family, it is the turn of Happy Jack
and Chatterer to learn about their family. Theirs is rather a large
family, and it is divided into three groups, the first of which
consists of the true Squirrels, to which group both Happy Jack and
Chatterer belong. The second group consists of the Marmots, and
Johnny Chuck belongs to this. The third group Timmy the Flying
Squirrel has all to himself."

"Where does Striped Chipmunk come in?" asked Chatterer.

"I'm coming to that," replied Old Mother Nature. "The true Squirrels
are divided into the Tree Squirrels, Rock Squirrels, and Ground
Squirrels. Of course Chatterer and Happy Jack are Tree Squirrels."

"And Striped Chipmunk is a Ground Squirrel," interrupted Peter,
looking as if he felt very much pleased with his own smartness.

Old Mother Nature shook her head. "You are wrong this time,