I think this question actually refers to a number of different myths and legends that are mentioned to us in Chapter Seven, which describes the way in which Nwoye is growing up and how he comes to spend more time with Ikemefuna and his father in Okonkwo's hut, listening to tales of battle, rather than the myths and legends he used to listen to in his mother's hut, even though he secretly still likes them. Notice how two separate stories are refered to in the following quote:
...but somehow he still preferred the storied that his mother used to tell, and which she no doubt still told to her younger children--stories of the tortoise and his wily ways, and of the bird eneke-nti-oba who challenged the whole world to a wrestling contest and was finally thrown by the cat.
As you can see, parables relating to a tortoise and a bird are remembered fondly by Nwoye, but they are also two separate parables rather than one parable that is told together. Like all of his mother's parables and stories, these seek to explain the world and why it is the way that it is through these colourful stories.