Experiments on the development of the ear of amblystoma punctatum.

Abstract

A series of experiments was performed during the years 1922-1925 on embryos of Amblystoma punctatum. Two main lines of investigation were carried out, namely, experiments to determine the limits of the regenerative capacity of the tissue surrounding the normal ear region, and experiments regarding the nature of the developing ear itself.

The first group involved extirpation of ectoderm in the ear region of embryos at different stages of development. The size of the pieces removed was 0.2 mm., 0.3 mm., 0.4 mm., 0.5 mm., and 0.6 mm., respectively. It was found that complete regeneration generally followed when the operation was performed on stages earlier than that in which invagination of the ectoderm had occurred. Regeneration was completely checked only by the removal of a piece of ectoderm 0.6 mm. in diameter, after a distinct auditory plate had formed.

A definite loss in the regenerative capacity of the surrounding ectoderm was evident, following invagination of the ear. The regenerated labyrinths were greatly reduced and, in several cases, no regeneration took place. Transplantation of undifferentiated ectoderm to the extirpated area caused a distinct lessening in regeneration in the earlier stages, and prevented it altogether in the later stages.

The second group of experiments dealt with the potencies of the ear at the time of invagination and at the time of closure of the vesicle. Experiments were performed involving removal of the anterior, posterior, dorsal and ventral halves of the ear respectively, at these stages, and it was found that while the remaining half, in 25 per cent of the cases formed a complete labyrinth, there was a tendency toward characteritstic defects following each type of operation. These defects were more constant at the later stages of operation.