  Diffusion of a polymer in a gel is studied within the framework of de Gennes'
model for reptation. Our results for the scaling of the diffusion coefficient D
and the longest relaxation time tau are markedly different from the most
recently reported results, and are in agreement with de Gennes' reptation
arguments: D ~ 1/N^2 and tau ~ N^3. The leading exponent of the finite-size
corrections to the diffusion coefficient is consistent with the value of -2/3
that was reported for the Rubinstein model. This agreement suggests that its
origin might be physical rather than an artifact of these models.
