In the next study, the Author examines the problem of probability associated with a mehanical system $\Sigma(x,y)$ whose definition is two differential equations of the first order, independent of time. We study the influence of the stability of the essential elements of the trajectories of $\Sigma$: (limit-cycles, singular points) on the nature of Fokker-Planck’s solutions of equation, associated with $\Sigma(x,y)$. It is proved that the density of probabilities is neither definite nor integrable to the singular stable points, and on the limit-cycles; then $\rho$ must have the structure of distributions. When $\Sigma$ is definite by differential equations with polynomes, the only case with density integrable is when there is just one single point which is a center.