  We report first results from a series of N-body/gasdynamical simulations
designed to study the origin of galaxy morphologies in a cold dark
matter-dominated universe. The simulations include star formation and feedback
and have numerical resolution sufficiently high to allow for a direct
investigation of the morphology of simulated galaxies. We find, in agreement
with previous theoretical work, that the presence of the main morphological
components of galaxies--disks, spheroids, bars--is regulated by the mode of gas
accretion and intimately linked to discrete accretion events. In the case we
present, disks arise from the smooth deposition of cooled gas at the center of
dark halos, spheroids result from the stirring of preexisting disks during
mergers, and bars are triggered by tides generated by satellites. This
demonstrates that morphology is a transient phenomenon within the lifetime of a
galaxy and that the Hubble sequence reflects the varied accretion histories of
galaxies in hierarchical formation scenarios. In particular, we demonstrate
directly that disk/bulge systems can be built and rebuilt by the smooth
accretion of gas onto the remnant of a major merger and that the present-day
remnants of late dissipative mergers between disks are spheroidal stellar
systems with structure resembling that of field ellipticals. The perplexing
variety of galaxy morphologies is thus highly suggestive of--and may actually
even demand--a universe where structures have evolved hierarchically.
