Yep, bugles (since they are valveless) are restricted to wavelengths (frequencies) which are integer fractions of the length of the bugle. It's really quite amazing the tunes which are played within that restriction.
From my tuba playing days I still remember the fractions....
first valve = 2 lengths,
second valve = 1 length,
third valve = 3 lengths,
and then the odd 4th valve was a more in tune 5 lengths.