On the interrelationships between morphology and movement in the tail of cichlid fish <i>Tilapia nilotica</i> (L.).

1. An account is given of the morphological structures in the tail region of the \"typical fish\" Tilapia nilotica (fam. Cichlidae), emphasizing the mechanical properties of the caudal skeleton, the vertical septum, the joints between the fin rays and the body, the muscles and tendons and the skin fascia. Two large cartilaginous plates, situated in the vertical septum, are described for the first time. 2. Detailed descriptions of the transformations of the caudal peduncle and fin during short series of lateral undulations of the body and fin are presented. 3. Mutual comparisons of the morphological descriptions with the descriptions of the movements show how structures in the tail are suited to the transfer of propulsive forces, generated by the oscillating tail fin, from the fin to the body. The way structures transfer oscillating movements from the body to the fin and the way muscle activity and several properties of the joints are able to affect the final form of the fin stroke are discussed. 4. A brief account is given of electromyographic data collected and of some problems concerning the use of electromyography in the tail region. 5. It is suggested that the skin fascia collaborates with the myotomes and myosepts to bend the body and the fin. ... Zie Summar