"The juvenile sea squirt wanders through the sea searching for a suitable rock or hunk of coral to cling to and make its home for life. For this task, it has a rudimentary nervous system. When it finds its spot and takes root, it doesn't need its brain anymore, so it eats it! (It's rather like getting tenure.)*"

* The analogy between the sea squirt and the associate professor was first pointed out, I think, by the neuroscientist Rodolfo Llinas.

-Daniel Dennett,
Consciousness Explained (1991)