Let us consider the cubic system of di_erential equations dx where Pi(x; y); Qi(x; y) are homogeneous polynomials of degree i in x and y with real coe_cients. The following GL(2;R)-comitants [1] have the _rst degree with respect to the coe_cients of the System. The de_nition of the transvectant of two polynomials is well known in the classical invariant theory. De_nition. Let f(x; y) and '(x; y) be homogeneous polynomials in x and y with real coeficients of the degrees is called the transvectant of the index k of the polynomials f and Remark.