Reversal of polarization in the ear primordium of Amblystoma punctatum (Linn.)

Abstract

The experimental studies of Harrison ( '24, '36) have revealed the existence of periods of axial polarization in the development of the internal ear of the salamander, Amblystoma punctatum (Linn.).During neural plate a i d fold stages, the ear ectoderm may be transferred t o the ear region of another embryo of thc same stage, and implanted on either side and in any orientation, with the subsequent formation of a normal (ipsolateral) ear.When embryos of the fused neural fold stage are utilized for transplantations, howe~cr, the ear ectoderm no Ionger reacts as readily to influences from its organic environment. The labyrinth which develops has its differentiated structures arranged either in the normal or the reversed order along the antcro-post erior (cephalo-caudal) asis, in accordance with the position of the ap axis of the graft in the host. These results may be interpreted as demonstrating the fixation of an ap polariz a t' ion.The results of transplantatioiis at slightly later stages, during invagination of the auditory cup, indicate that a similar fixation of the clorso-ventral polarization occurs a t this time.After this, the ear vesicle gradually hecoines transformed into a mosaic of regions, each determined to differentiate into a particular portion of the labyrinth (Kaan, '26). 141