  We present a near-infrared extinction study of nine dense cores at
evolutionary stages between starless to Class I. Our results show that the
density structure of all but one observed cores can be modeled with a single
power law rho \propto r^p between ~ 0.2R-R of the cores. The starless cores in
our sample show two different types of density structures, one follows p ~ -1.0
and the other follows p ~ -2.5, while the protostellar cores all have p ~ -2.5.
The similarity between the prestellar cores with p ~ -2.5 and protostellar
cores implies that those prestellar cores could be evolving towards the
protostellar stage. The slope of p ~ -2.5 is steeper than that of an singular
isothermal sphere, which may be interpreted with the evolutionary model of
cores with finite mass.
