The location of the optic anlage in Amblystoma and the interpretation of certain eye defects

Abstract

The early embryos of Amblystoma were operated upon so as to remove definite areas from the open medullary plate in order to determine the position of the materials which would give origin to the future eyes.

Preliminary experiments of sticking and disturbing the cells in the anterior end of the medullary plate without actually removing these cells did not prevent the subsequent development of the optic vesicles in an apparently normal manner. Cutting out rectangular pieces of the anterior part of the medullary plate, reversing the pieces and transplanting them merely caused the eyes to develop in misplaced positions. These two experiments demonstrate the fact that unless the future eye material is well removed by the operation the optic vesicles may form. This fact is important in considering the results of the following experiments.

A general statement of the results of the experiments may be expressed as follows: Thirty embryos studied after various operations in which lateral portions of the medullary plate were removed at slightly different developmental stages showed in twenty-four individuals, or eighty per cent. of the cases, subsequent development of both eyes, while only six specimens, or twenty per cent.

of the cases, showed absence of the eye. In one case the presence of the eye was questionable, in five cases one eye and in one case both eyes were absent. The absence of the eyes in the latter cases was possibly due to the cut having been made in a more median position than was intended.

Nine embryos studied after having been operated upon so as to remove a narrow median strip of cells from the anterior portion of the medullary plate showed in four cases, or about forty-five per cent. of the specimens, entire absence of eyes.