The extremely red stars are all faint, only a very few being visible to the naked eye, and these near the limit of vision. Our knowledge concerning them is relatively limited. That these, and all stars, will become invisible to our telescopes, and ultimately be dark unshining bodies, is the logical conclusion to which the evolutionary processes will lead. As I have already stated, both Newcomb and Kelvin were inclined to believe that the major part of gravitational matter in the universe is already invisible. It should be said that a few astronomers doubt whether the order of evolution is so clearly defined as I have outlined it; in fact, whether we know even the main trend of the evolutionary process. We occasionally encounter the opinion that the subject is still so unsettled as not to let us say whether the helium stars are effectively young or the red stars are effectively old. Lockyer and Russell have proposed hypotheses in which the order of evolutionary sequence begins with comparatively cool red stars and proceeds through the yellow stars to the very hot blue stars, and thence back through the yellow stars to cool red stars. I think the essentially unanimous view of astronomers is to the effect that the great mass of accumulated evidence favors the order of evolution which I have described. We are all ready to admit that there are apparent exceptions to the simple course laid down, but that these exceptions are revolutionary in effect, and not hopeless of removal, has not yet, in my opinion, been established. PHYSICAL CONDITIONS GOVERN APPEARANCES OF SPECTRA