I can read them normally within Calibre on my desktop, I have no other readers because normally I don't read epubs (indeed that is what they are) on my Mac.
With extracts it's simple, every chapter on my Ipad only shows 1 or 2 pages whereas within Calibre it shows the complete chapters, on my desktop that is.
That's what I call weird, I have the complete epub untill I move it to my Ipad, then it's a lot less, if you want to show someone a short preview of a ebook this is a perfect way of showing it.
It all used to be perfect untill some weeks ago when it suddenly happened to me
sad isn't it??
I allways use the latest version of Calibre, if this any help.