suspensions of self-catalythic Janus colloids [@Palacci2010] and motile epithelial cell sheets such as those studied in wound healing assays [@Saez2007; @Petitjean2010]. Self-propelled nematics therefore represent an important new class of active systems of direct experimental relevance.

A useful theoretical framework for describing the collective behavior of active systems is a continuum model that generalizes liquid crystal hydrodynamics to include new terms induced by activity  [@Simha2002; @Kruse2004; @Voituriez2005; @Voituriez2006; @Marenduzzo2007; @Giomi2008; @Cates2008; @Sokolov2009; @Giomi2010; @Saintillan2010]. In this paper, we consider a minimal phenomenological continuum model of self-propelled nematics based on the equations derived by us from a microscopic model of SP hard rods. We show that in these systems it is important to explicitly retain the dynamics of both the collective velocity or polarization field of the particles and of the nematic order parameter to unfold the mechanisms at play in the formation of emergent structures. Further, we show that *all* active nematics (both consisting of shakers and SP particles) exhibit the phenomenon of dynamical self regulation, due to the fact that the parameter controlling the order-disorder transition, namely the density $\rho $ of active particles, is not externally tuned, as in systems undergoing equilibrium phase transitions, but it is dynamically 