  Developing recently proposed constructions for the description of particles
in the $(1/2,0)\oplus (0,1/2)$ representation space, we derive the second-order
equations. The similar ones were proposed in the sixties and the seventies in
order to understand the nature of various mass and spin states in the
representations of the $O(4,2)$ group. We give some additional insights into
this problem. The used procedure can be generalized for {\it arbitrary} number
of lepton families.
