2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/66892The main purpose of this paper is twofold. We first want to analyze in details the meaningful geometric aspect of the method introduced in the previous paper [12], concerning regularity of families of irreducible, nodal "curves" on a smooth, projective threefold $X$. This analysis highlights several fascinating connections with families of other singular geometric "objects" related to $X$ and to other varieties. Then, we generalize this method to study similar problems for families of singular divisors on ruled fourfolds suitably related to $X$.22 pages, Latex 2e, submitted preprintAlgebraic Geometry14H10, 14J30, 14J60, 14J35, 14C20text