I discuss the formation of the modern cosmological paradigm. In more detail I describe the early study of dark matter and cosmic web and the role of Yakov Zeldovich in the formation of the present concepts on these subjects.

We compare the characteristics of stellar populations with those of dark halos. Dark matter around galaxies, and in groups, clusters and voids is discussed. Modern data suggest that the overall density of matter in the Universe is ΩM = 0.3 ± 0.1, about 80 % of this matter is nonbaryonic dark matter, and about 20 % is baryonic, mostly in the form of hot intra-cluster and intragroup gas, the rest in stellar populations of galaxies. All bright galaxies are surrounded by dark matter halos of external radii 200 − 300 kpc; halos consist mostly of non-baryonic matter with some mixture of hot gas. The Universe is dominated by dark energy (cosmological constant) term. Dark matter dominates in the dynamical evolution of galaxies in groups and clusters.

Generally the density of the environment is important for the formation and evolution of galaxies: bright elliptical galaxies reside in the centers of galaxy clusters, whereas late type galaxies preferentially populate small groups, filaments or the outskirts of rich clusters of galaxies. Furthermore, fainter galaxies define smaller voids than bright galaxies. Our investigation of void catalogues in the Northern Local Void region shows that large voids are interlaced by systems of faint galaxies dividing them into smaller subvoids (Lindner et al., 1995). This void hierarchy is an important property of the Large Scale Structure in the nearby Universe and can help to solve problems concerning the distribution of dwarf galaxies and BCDGs.

The spatial distribution of galaxies is compared with model distributions. It is demonstrated that giant and dwarf galaxies in the Local Supercluster occupy statistically identical regions. Various tests suggest that galaxy formation is biased since all unbiased model distributions are in conflict with observed distribution of galaxies. Multifractal analysis shows that a cold dark matter dominated universe with biased galaxy formation has a fairly constant fractal dimension over a broad range of scales. This contrasts with the observed distribution which does not show simple fractal features.

To study distribution of galaxies and voids, the rectangular box under study is divided into cubic cells, and mean density of particles in cells is derived. For any density level cells can be divided into ‘filled’ or ‘empty’ ones if their density is higher or lower than a threshold density. The length and volume of the largest connected system, as well as the number of systems of connected cells are derived for observed, model and random samples. The comparison of results demonstrates that galaxy formation is biased, supercluster-void topology is sponge-like in a wide threshold density interval, and that there are no isolated galaxies in voids.

A review of observational work on dark matter in USSR is given. Dynamically the dark matter can be located (i) in the galactic disk and/or in dwarf galaxies, (ii) in coronas of galaxies and in clusters of galaxies, and (iii) distributed smoothly in voids. The possible amount of matter in all three forms is discussed. Physically dark matter can be baryonic or non-baryonic, in the latter case either hot, warm or cold. Available information on the nature of dark matter is indirect, coming from theories of the formation of structure in the Universe. Two constraints to the formation scenarios are discussed, the galaxian correlation function and their morphology.

Most galaxies with UV-continuum avoid clusters of galaxies (Lipovetsky 1986). Until recently, however, it was difficult to compare spatial distribution of galaxies with UV-continuum with galaxies of other morphological types, since the number of galaxies with known distances was too small. Rapid accumulation of complete redshift samples in large areas of sky (Huchra 1985) makes such study now possible.

Abell and Corwin (34.160.040) have continued the search of southern clusters on photographs taken with the U.K. Schmidt telescope at Siding Spring. A catalogue is in preparation, it continues the Abell catalogue toward southern declinations. West (32.160.019, 32.160.036, 34.160.044) has initiated a study of distant southern clusters with automatic identification of clusters and objective evaluation of their properties. Noonan (30.160.006) and Sarazin et al. (31.160.030) have listed clusters with published redshifts. Numerical simulations have demonstrated the presence of bias in observed clusters as difined by Abell (33.160.006), ranked absolute magnitudes of galaxies are distance dependent (33.160.081), some clusters may be due to projection effects (34.160.009).

As demonstrated by de Vaucouleurs (1956, 1975a, b, 1976), Abell (1961), Karachentsev (1966), Kiang and Saslaw (1969) and others, clusters of galaxies as well as groups of galaxies have a tendency to form second-order clusters of galaxies, often called superclusters. Recent statistical studies by the Princeton group (Davis, Groth and Peebles 1977, Seldner and Peebles 1977a) have confirmed this result. Statistical studies, however, give little information about the internal structure of second-order clusters.

“Galaxies are like people: they depend on both genetics and environment” (van den Bergh 1975)

Mass-to-luminosity ratios of systems of galaxies as derived by different authors have a large scatter from ~ 10 to ~ 200. the observational data used by different authors differ only slightly, so the differences should lie in the treatment of the data. We have found that in most cases < M/L > differences can be explained in the following ways.