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We present a comprehensive analysis on the evolution of envelopes surroundingprotostellar systems in the Perseus molecular cloud using data from the MASSESsurvey. We focus our attention to the C$^{18}$O(2--1) spectral line, and wecharacterize the shape, size, and orientation of 54 envelopes and measure theirfluxes, velocity gradients, and line widths. To look for evolutionary trends,we compare these parameters to the bolometric temperature Tbol, a tracer ofprotostellar age. We find evidence that the angular difference between theelongation angle of the C$^{18}$O envelope and the outflow axis directiongenerally becomes increasingly perpendicular with increasing Tbol, suggestingthe envelope evolution is directly affected by the outflow evolution. We showthat this angular difference changes at Tbol = $53 \pm 20$ K, which includesthe conventional delineation between Class 0 and I protostars of 70K. Wecompare the C$^{18}$O envelopes with larger gaseous structures in othermolecular clouds and show that the velocity gradient increases with decreasingradius ($|\mathcal{G}| \sim R^{-0.72 \pm 0.06}$). From the velocity gradientswe show that the specific angular momentum follows a power law fit $J/M \proptoR^{1.83 \pm 0.05}$ for scales from 1pc down to $\sim$500 au, and we cannot ruleout a possible flattening out at radii smaller than $\sim$1000 au.

Evolution and Kinematics of Protostellar Envelopes in the Perseus Molecular Cloud