  We obtain Gaussian upper and lower bounds on the transition density q_t(x,y)
of the continuous time simple random walk on a supercritical percolation
cluster C_{\infty} in the Euclidean lattice. The bounds, analogous to Aronsen's
bounds for uniformly elliptic divergence form diffusions, hold with constants
c_i depending only on p (the percolation probability) and d. The irregular
nature of the medium means that the bound for q_t(x,\cdot) holds only for t\ge
S_x(\omega), where the constant S_x(\omega) depends on the percolation
configuration \omega.
