The general structure of the galaxies is extremely diverse and can be described by Hubble's classification only in the first approximation. In fact, the differences in the distribution of gas and dust in some galaxies which have been established recently, the evident dissimilarity of the intensity of the radio emission in individual galaxies, as well as other facts, suggest definite differences even among galaxies belonging to the same type according to Hubble. Hubble's classification gives a sufficiently exhaustive description of the diversity of the optical forms of galaxies and unites them in a single sequence, which, in the case of spirals, branches into two parallel sequences (ordinary and barred spirals). The interpretation of Hubble's sequence as an evolutionary one became rather popular. In this case usually either the Eo form is considered as the initial stage (Jeans, Hubble) or, conversely, the irregular galaxies and late spirals are considered as the initial stage with the elliptical galaxies being the late stage of evolution (Shapley and many others).