the story of snail

Many years ago, I read a story about snail. It's very meaningful.

One day, a young snail ask his mother:"Why we must ??? the shell when we born?"
Mother:"Because me didn't have bones to support our body, we just can creep and slowly, so we need the shell to protect us."

snail:"But why caterpillar didn't have the too heavy, too hard shell? they also didn't have bones and creep slowly."
mother:"Because they can to be a butterfly, the sky will protect them."

snail:"The earthworm didn't have bones, creep slowly and can't to be a butterfly. why they also don't have the too heavy, too hard shell?"
mother:"Because they can drilled in earth, the earth can protect them."

the snail crying:"why just we are so pitiful? the sky and the earth do not protect us."
mother:"So we have the shell. we don't depend on the sky, we also don't depend on the earth,we depend on ourselves."