Biology

I've been studying like crazy for a Biology test lately, and my best friend for the topic at hand is the Idiot's Guide to Biology (much different from Biology for Dummies).  Still, even at its simplified level, there are a few things the book cannot explain to me, such as why they didn't get a better editor before sending it off to printing.

Take note--they're explaining what makes a fish a fish.  Their list begins with this:

1. Jaws (except for the jawless fish)

If a fish must have everything on the list to be considered a fish, isn't the very first point kind of pointless?  That's like saying "Paper must be flat to be considered paper, except in the case of not-flat-paper." Or, "Socks must go on feet, unless they go on hands."  And maybe even, "A blog must be educational, unless it is just plain stupid." (That one describes this pretty well, actually.)

If I've got to remember all these strange paradoxes for the test, I might be out of luck.