Alternatively, under the File menu Check Host for New Mail will also do it.

I am new to Pegasus and this posting will probably seem ridiculous to experienced users, but although Pegasus downloaded a few emails when I first installed it, it has not downloaded any more since.  Every other email client I have come across has a button called "Get Mail", "Fetch Mail", Get Messages" or something like that, but I can't find anything of the sort on Pegasus.  Could one be added?  Or am I just missing something blindingly obvious?

Hi Trumpeter,

You can find some icons with a globe; you can use the one with the red arrow (Check your POP3 host for new mail).
That will do, I think.