  We derive the proper motions, membership probabilities, and velocity
dispersions of stars in the regions of the young (about 2-4 Myr-old) open
clusters NGC 2244 (the central cluster in the Monoceros R2 association) and NGC
6530 (the dominant cluster in the Sgr OB1 association) from photographic plate
material obtained at Shanghai Astronomical Observatory, with time baselines of
34 and 87 years, respectively. Both clusters show clear evidence of mass
segregation, but they do not exhibit any significant velocity-mass (or,
equivalently, a velocity-luminosity) dependence. This provides strong support
for the suggestion that the observed mass segregation is -- at least partially
-- due to the way in which star formation has proceeded in these complex
star-forming regions (``primordial'' mass segregation). Based on arguments
related to the clusters' published initial mass functions, in conjunction with
our new measurements of their internal velocity dispersions (35 and 8 km/s for
NGC 2244 and NGC 6530, respectively), we provide strong arguments in favor of
the dissolution of NGC 2244 on very short time-scales, while we speculate that
NGC 6530 may be more stable against the effects of internal two-body
relaxation. However, this latter object may well be destroyed by the strong
tidal field prevalent at its location in the Galactic plane in the direction of
the Galactic Center.
