The continuation of the other author's work - intertextual literary genre or a form of cultural parasitism?

Commercialization of art is conducive to a popularity of productions sequel type, productions that correspond to a mass audience taste. A substantial majority of the examples shows that the level of the dependence of continuation on the model calls individuality of the work into question. When authors adopt someone else's heroes, along with their surroundings, and when restrict artistic efforts to invent new links of a plot, they seldom go beyond a cultural parasitism of a cultural parasitism. However among continuations of the famous works of literature one may find examples that pretend to be perceived as original authorial projects in which a complementation of the work of the other author is artistically functionalized, subdued to own vision of the world and ideas. The paper considers - using a few examples from Polish and Russian literature - a question, if it is possible to analise the continuation of the plot as one of the 'intertextual genres', i.e. works in which the structure and the meanings base on a direct relation to things that have already been written.