ABSTRACT. The properties of the identity embedding operator I(X1, )(2) (X1 C X2) between symmetric function spaces on [0, 1] such as weak compactness, strict singularity (in two versions), mad the property of being absolutely summing are examined. Banach and quasi-Banach spaces are considered. A complete description of the linear hull closed with respect to measure of a sequence (g(r)) of independent symmetric equidistributed random variables with 1 d(g(nr) ; t) = meas(w : "--Ig~,' )(0~)l > t) = ~ for t >_ 1 and 0 < r < co is obtained, and the boundaries for this space on the scale of symmetric spaces are found.