Determination of the ear and side=specificity of the ear region ectoderm in amphibian embryoes.

Abstract

1. The ectoderm of the presumptive ear region h as been determined at the stage of earliest appearance of the neural folds.2. The ectoderm of the presumptive earre gion can differentiate into au ear either in the same region of the other side or in quite an indifferent region. Iii the later case the ear is deformed.3. The characteristic development of the ectoderm of the presumptive ear region is dependent to some extent on the surrounding tissue.4. The earplateless epithelium can develop a more or less complete ear.5.The earplate alone without overlying epithelium caii form an ear when grafted on an indifferent regimi.6. The anlage of the endolymph atic sac can differentiate further in an indifferent region and caii normally secrete lime without any connection to the labyrinth.7. Lack of cartilage around the endolynaphatic sac is due to the nature of the sac itself, but not to its anatomical relation to the brain. s. At the earliest appearance of the neural folds the removal of mm square of ectoderm from the ear region was followed by 100%regeneration of the ear.8. At the closure of the neural folds no regeneration took place after the above operation.10. Grafting a regenerated ear vesicle on the ear region of the other side is followed by the development of a very defective ear.11. In presumptive ear ectoderm at the stage of earliest ap pearance of the neural folds the side of the ear is not yet determined.12. After autoplastic transplantation of the ectoderm of the ear region at the stage of closure of the neural folds the right side ectoderm resulted in the formation of right side ear on the left side.13. Thus at the stage of closure of the neural folds the ectoderm of the presumptive ear region is already determined as to the side.14. The regenerated ear vesicle seems in the beginning not definitely determined as to its side. Therefore such determination ought to occur later in the regenerated ear vesicle than in the normal.15. The earplatelessear region epithelium seems to he not definitely determined as to its side.