  We report evidence from the 3B Catalogue that long ($T_{90} > 10$ s) and
short ($T_{90} < 10$ s) gamma-ray bursts represent distinct source populations.
Their spatial distributions are significantly different, with long bursts
having $\langle V/V_{max} \rangle = 0.282 \pm 0.014$ but short bursts having
$\langle V/V_{max} \rangle = 0.385 \pm 0.019$, differing by $0.103 \pm 0.024$,
significant at the $4.3 \sigma$ level. Long and short bursts also differ
qualitatively in their spectral behavior, with short bursts harder in the BATSE
(50--300 KeV) band, but long bursts more likely to be detected at photon
energies > 1 MeV. This implies different spatial origin and physical processes
for long and short bursts. Long bursts may be explained by accretion-induced
collapse. Short bursts require another mechanism, for which we suggest neutron
star collisions. These are capable of producing neutrino bursts as short as a
few ms, consistent with the shortest observed time scales in GRB. We briefly
investigate the parameters of clusters in which neutron star collisons may
occur, and discuss the nuclear evolution of expelled and accelerated matter.
