2. In the long run, we must expect the stars to grow colder, at least as to the surface strata. What the average interior temperatures are is another question; the highest interior temperatures are thought to be reached at an intermediate or quite late stage in the process, in accordance with principles investigated by Lane and others; but the temperatures existing in the deep interiors seem to have little direct influence in defining the spectral characters of the stars, which are concerned more directly with the surface strata.[1] We should therefore expect the simpler types of spectra, such as we find in the helium and hydrogen stars, in the early stages of the evolutionary process. The complicated spectra of the metals, and particularly the oxides of the metals, should be in evidence late in stellar life, when the atmospheres of the stars have become denser and colder. [1] This important point seems not to have been realized by all theorists. 3. The velocities of the Orion nebula, the Trifid nebula, the Carina nebula, and of several other irregular nebulae, have been measured with the spectroscope. These bodies seem to be nearly at rest with reference to the stellar system. The helium stars have the lowest-known stellar velocities, and the average velocities of the stars are higher and higher as we pass from the helium stars, through the hydrogen and solar stars, up to the red stars. The average velocities of the brighter stars of the different spectral classes, as determined with the D. O. Mills spectrographs at Mount Hamilton and in Chile, are as in the following table: Spectral No. of Class Stars Average Velocity in Space B 225 12.9 km. per Sec. A 177 21.9 F 185 28.7 G 128 29.9 E 382 33.6 M 73 34.3 We can not place the irregular nebulae after the red stars: their velocities are too small, and their spectra have no resemblances to the red-star spectra. 4. Wherever we find large irregular gaseous nebulae we find stars in the early subdivisions of the helium group. They are closely related in position. This is true of the Orion and other similar regions. The irregular, gaseous nebulae are in general found in and near the Milky Way, and so are the helium stars. The yellow and red stars, at least the brighter ones, do not cluster in nebulous regions.