This paper considers the statistical theory of cosmogonical bodies formation in order to derive equations for the gravitational field of a condensing cosmogonical body. Starting the conception for forming a spheroidal body inside a protoplanetary nebula, this theory solves the problem of gravitational condensation of such cloud with the point of view to planetary formation in its own gravitational field. Within the framework of the statistical theory, the new models and evolutional equations of the statistical mechanics have been obtained. As shown in this paper, the presence of a dark matter (or an ethereal medium) around gravitationally interacting masses serves as the basis for their gravitational interactions and gravitational wave propagation. First, equation of motion of a “liquid” particle in the “quasi-solid” approximation inside a spheroidal body in gravitational and inertial fields is considered. Using the vector gravimagnetic potential introduced the equation of moving solid particle with an ethereal surrounding in gravitational and gravimagnetic fields is obtained. Taking into account this equation the first system of equations of the gravitational/gravimagnetic field is derived. Using both Lagrange function of a moving “liquid” gaseous–ethereal particle (with a “solid” core) in the gravitational/gravimagnetic field and Lagrange function of the same field, the expression of a total action for the gravitational/gravimagnetic field and matter is obtained. Applying the principle of least action and varying only the gravitational potentials together with the anti-diffusion velocity (but not the coordinates) the second system of equations of the gravitational/gravimagnetic field of a condensing spheroidal body is derived. Using these equations, the propagation of plane monochromatic gravitational waves in a gravitational field of a condensing cosmogonical body is studied. It is shown the Jeans’ criterion of gravitation instability takes place in this case.