forms of matter. Axisymmetric collapse of gravitational waves was shown to have a $\gamma$ of about 0.36, and $\Delta \simeq 0.6$. For spherical collapse of radiation (perfect fluid with equation of state $p=\rho/3$) the critical solution has continuous self-similarity, and $\gamma$ of about 0.36. However it has become clear now that the critical exponent $\gamma$ is not independent of the choice of matter. A study of collapse for a perfect fluid with an equation of state $p=k\rho$ shows that $\gamma$ depends on $k$. For a given form of matter, there appears to be a unique $\gamma$, but the value changes as the form of $T_{ik}$ is changed.

An important issue regarding the solutions with $p>p_{*}$ is the following. These solutions are identified as black holes because of the presence of an apparent horizon. However, current numerical studies do not probe the singularity itself, and one cannot for now rule out the possibility that the the solutions with $p>p_{*}$ fall into two classes: (a) those which have a Cauchy horizon lying outside the apparent horizon, and hence are naked singularities, and (b) those which are black holes. There is actually some evidence for this in the work of Brady [@br], and 