The electric polarization patterns existing in the appendicular skeleton of the Amphibia, Reptilia, Aves and Mammalia, and the changes they undergo in the course of ontogenesis, have been made the object of detailed investigations. There are two distinct directions of electric polarization in the long bones of the appendicular skeleton: 1. One parallel and 2. one at right angles to the longitudinal bone axis, i. e. the course of the collagen fibrils. These are called “longitudinal polarization” and ”radial polarization” in this study. The present paper is exclusively concerned with the longitudinal polarization of the appendicular skeleton and the changes which affect it in the course of phylogenesis and ontogenesis. In all the Tetrapoda we investigated, the longitudinal electric polarization in the long bones was found to have the same characteristic pattern in the initial stages of ontogenesis. In the Crocodilia, Aves and Mammalia, the original directions of longitudinal polarization gradually become reversed by 180° during the individual's growth period. On termination of longitudinal growth of the long bones, the reversal process is either complete or has reached a very advanced stage. In the latter case, reversal is completed in the subsequent stages of ontogenesis. It is thus seen that the process taking place in the appendicular skeleton of the higher tetrapods is similar to that previously noted in the bony structures of the human axial skeleton and that of the other Mammalia. The transformation phenomena of longitudinal electric polarization are demonstrated with the aid of examples chosen from the various classes of vertebrates. The reversal of the directions of polarization either sets in from the centre of the diaphysis or it emanates from its two ends. In the skeleton of the rear extremity, the reversal took place in a regular sequence in all the cases we investigated, namely: Phalanges-metatarsal bones-tibia/fibula-femur. This corresponds to the well-known order of epiphyseal ossification in the extremities of the various Mammalia. Details are given of the special patterns of electric polarization encountered in the epiphyses of the Amphibia, Reptilia, Aves, Monotremata and Marsupialia.