Annie has seen a lot of fascinating animals on her many little excursions, but there are still many she's only read about in books that she would very much like to see. In particular, she wants to see what she calls the famous amoeba, a one-cell organism that reproduces by changing its shape.

But this proves to be easier said than done. Annie looks in all the places where the amoeba might be found. She looks in the hay infusion but can't find him there. And he's nowhere to be found in any warm ponds and streams, as a cold winter in Pittsburgh has ensured that there aren't any in the local vicinity.

But eventually, in late spring, Annie finally catches a break. She gathers a sample of some dirty, scummy puddle water from Frick Park. She takes it home in a jar and leaves it to fester there for a while.

One June night after dinner, Annie heads down to the basement and puts a drop of the puddle water on a slide that she proceeds to examine with her microscope. Much to her delight, she sees the famous amoeba, “as blobby and grainy as his picture.” Annie would recognize him from anywhere.