An "entozoon" seems to the practical man a foolish, imaginary creature.    From Wordnik.com.  [Editorials from the Hearst Newspapers] Reference

When you know the entozoon you can dig him out and save the sheep's life.    From Wordnik.com.  [Editorials from the Hearst Newspapers] Reference

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.    From Wordnik.com.  [Two Trips to Gorilla Land and the Cataracts of the Congo Volume 2] Reference

A disorder known as "the staggers," of which many thousands of sheep have died annually, is caused by an entozoon which presses on the brain, and that if the creature is extracted through the softened place in the skull which marks its position, the sheep usually recovers, is another debt which agriculture owes to biology.    From Wordnik.com.  [Essays on Education and Kindred Subjects Everyman's Library] Reference