Unfortunately, that text is missing in my book as well. The first sentense of that paragraph ends in "key signature." He's saying that they are always shown in the sequence that follows, first F, then C, then G, then D, then A, then E, then B... and then... lol. Sorry lol. To recap, the order of sharps is F,C,G,D,A,E,B. The order of flats is the reverse (B,E,A,D,G,C,F). Key signatures are always written the same way, and there is an order to them...
I wrote out thier relationship a while ago, when I was learning scales. Turns out it also helps you remember the perfect fifths (a.k.a. dominant) of every scale (since thats how the next scale is chosen).
Image of the Major Scales written in steps...
bigger sized version, just in case... http://s92413871.onlinehome.us/images/major_scales.jpg
To get a scale that is not written there (i.e F Natural, or D Flat) just "multiply" through, with a flat, any of the scales written there and you will have your scale.
Notice that the Major scale is two identical scales back to back. This is why there is such a strong rlelation between dominant and tonic... because a dominant of a given major scale is the tonic of the following major scale.
Anyways, the missing words dont seem to be of crucial importance. I do hope it doesnt happen elsewhere in the book though.