We study a Siegel superparticle moving in flat superspace. Canonical quantization is accomplished yielding the massless Wess-Zumino model as an effective field theory. The path integral representation for the corresponding superpropagator is constructed and proven to involve the Siegel action in a gauge-fixed form. It is shown that higher-order fermionic constraints intrinsic in the theory, though being a consequence of others in d = 4, make a crucial contribution to path integral.