The chondrocytes of the metamorphosing cartilage exhibit an extensive granular reticulum, apparently in connection with the increasing intercellular substance and the building of the bearing construction of the cartilage. For a limited time a GOLGI-apparatus appears, which subsequently disappears. Then the cell hypertrophies and an opening zone is built up. By means of the regression of this zone the cavity of ossification center is enlarged. The fibril structure is characterized by a reticular system. In the spaces the proteoglycans are deposited. In compound with the tensile strength of fibrils arise the elastic comprehensive strength of cartilage. The nature of fibrils varied in respect of their diameter (80 to 900 A) and the dimension of their period.