  We show how the multiloop amplitudes of $\Phi^3$ theory (in the worldline
formulation of Schmidt and Schubert) are recovered from the N-tachyon
$(h+1)$-loop amplitude in bosonic string theory in the $\alpha' \to 0$ limit,
if one keeps the tachyon coupling constant fixed. In this limit the integral
over string moduli space receives contributions only from those corners where
the world-sheet resembles a $\Phi^3$ particle diagram. Technical issues
involved are a proper choice of local world-sheet coordinates, needed to take
the string amplitudes off-shell, and a formal procedure for introducing a free
mass parameter $M^2$ instead of the tachyonic value $-4/\alpha'$.
