What is the significance of some of the animals they discuss in Things Fall Apart?

Okonkwo talks of his self-sufficiency by using the story of a lizard. 'The lizard that jumped from the high iroko tree to the ground said he would praise himself if no one else did.' There is also the story of the tortoise meant to teach the children a lesson. Tortoise tricks birds into giving him wings, but when he steals food from them, they take away his wings and he falls. The fall breaks his shell and it has to be glued together, which is why it looks the way it does.