The basic ideas in this paper are described in recently published papers by Ahern et al. (1977) and Kwok (1977). There are two main points to be made in addition, which remove the differences between these two papers.

The mass-luminosity relation for single-mode Cepheids obtained by Saio, Kobayashi, and Takeuti (1977) indicates that the masses of classical Cepheids seem to be less than those that result from evolutionary calculations without substantial mass loss. The mass loss rate at the red giant phase should be 10−5 solar masses per year. Some of the beat Cepheids seem to form a group among the variable stars.

This paper serves two purposes: 1) to discuss the latest improvements in nonlinear pulsation theory indicating the ability to resolve features such as the “Christy bump” on the light curves and 2) to show from the results of a bump model and recent observations that mass loss is one of the possible explanations for the mass discrepancy problem between evolutionary and pulsation theories. Recent observations by Sanford and Gow of Los Alamos and Bernat (McDonald Observatory) show that extensive mass loss has occurred in the evolution of the M supergiant α Orionis.

The purpose of this communication is to show that one possible explanation for the asymmetric line profiles observed in β Canis Majoris stars may be the presence of a stellar wind superimposed on a radial or nonradial pulsation.

The effects of the interaction of strong Wolf-Rayet stellar wind with the surrounding interstellar medium in ring-type nebulae are briefly discussed.

The outstanding variability of the envelope of the WN 7 star HD 151932 is explained by small density fluctuations. Variable WR wind may be the reason for the filamentary structure observed in ring-type nebulae.

The continuous energy distribution of ρ Cas obtained in the wavelength range 340 - 710 nm has been compared with the energy distribution of δ CMa in the same wavelength range. The circumstellar shell associated with ρ Cas seems to modify the continuum of the star appreciably. Variations in the Balmer emission of ρ Cas taking place within a day are noticed.

Mass loss from stars returns processed as well as unprocessed material to the Interstellar medium, and thus enriches it in helium and heavy elements. In this very brief review we outline the theory of the chemical evolution of the interstellar medium.