  Using the the theory of FS^op modules, we study the asymptotic behavior of
the homology of $\overline M_{g,n}$, the Deligne--Mumford compactification of
the moduli space of curves, for $n >> 0$. An FS^op module is a contravariant
functor from the category of finite sets and surjections to vector spaces. Via
maps that glue on marked P^1's, we give the homology of $\overline M_{g,n}$ the
structure of an FS^op module and bound its degree of generation. As a
consequence, we prove that the generating function $\sum_{n} \dim(H_i(\overline
M_{g,n})) t^n$ is rational, and its denominator has roots in the set $\{1, 1/2,
\dots, 1/p(g,i)\}$ where $p(g,i)$ is a polynomial of order $O(g^2 i^2)$. We
also obtain restrictions on the decomposition of the homology of $\overline
M_{g,n}$ into irreducible $S_n$ representations.
