entozoon

An "entozoon" seems to the practical man a foolish, imaginary creature.

It is a semi-transparent entozoon; each segment is long compared to its breadth, and narrowed at both ends.

The entozoon of course gives rise to a variety of stale and melancholy jokes about the early bird, the worm that dieth not, and so forth.

When you know the entozoon you can dig him out and save the sheep's life.