  In this paper we present a geometric way to extend the Shintani lift from
even weight cusp forms for congruence subgroups to arbitrary modular forms, in
particular Eisenstein series. This is part of our efforts to extend in the
noncompact situation the results of Kudla-Millson and Funke-Millson relating
Fourier coefficients of (Siegel) modular forms with intersection numbers of
cycles (with coefficients) on orthogonal locally symmetric spaces. In the
present paper, the cycles in question are the classical modular symbols with
nontrivial coefficients. We introduce "capped" modular symbols with
coefficients which we call "spectacle cycles" and show that the generating
series of cohomological periods of any modular form over the spectacle cycles
is a modular form of half-integral weight. In the last section of the paper we
develop a new simplicial homology theory with local coefficients (that are not
locally constant) that allows us to extend the above results to orbifold
quotients of the upper half plane.
