  The topology of large scale structure is studied as a function of galaxy type
using the genus statistic. In hydrodynamical cosmological CDM simulations,
galaxies form on caustic surfaces (Zeldovich pancakes) then slowly drain onto
filaments and clusters. The earliest forming galaxies in the simulations
(defined as ``ellipticals") are thus seen at the present epoch preferentially
in clusters (tending toward a meatball topology), while the latest forming
galaxies (defined as ``spirals") are seen currently in a spongelike topology.
The topology is measured by the genus (= number of ``donut" holes - number of
isolated regions) of the smoothed density-contour surfaces. The measured genus
curve for all galaxies as a function of density obeys approximately the
theoretical curve expected for random-phase initial conditions, but the early
forming elliptical galaxies show a shift toward a meatball topology relative to
the late forming spirals. Simulations using standard biasing schemes fail to
show such an effect. Large observational samples separated by galaxy type could
be used to test for this effect.
