Mononuclear and multinuclear chondroclasts as well as osteoclasts and their involvement into the processes of replacement of provisional cartilaginous skeleton by definitive bony one were cytogenetically studied during ontogenesis of terrestrial vertebrates (amphibians, reptiles, birds, and mammals). It was detected that mononuclear and multinuclear clastic cells were distinctive morpho-functional forms. The former are capable to resorb only non-calcified hyaline cartilage, the latter are capable to resorb only calcified tissues (cartilage, bone). The mechanisms of tissue resorption performed by these cells are discussed.