Space is a cubic lattice of points with eight positions in each cell. — This proposition leads, in the limit of an infinite number of points and a vanishing lattice constant, to a Lorentz invariant Schrodingerian for motion if we assume, that only one kind of urfermions exists, and that transitions are possible only to next neighbours. Best adapted to the lattice is an interaction operator which is essentiallyHeisenberg's. In HF-approximation we derive the equations for the masses of quasi particles in the liquid of urfermions. In the now proposed lattice the masses are finite, if and only if the same is true for the interaction constant. We obtain the energyE=±√k 2+m 2 and the massm=2.757W even in the limit. It is easy to see, why now we need only a finite value ofW.