Electroretinogram of the frog during embryonic development.

Eyes removed from frog embryos at various stages of development gave a definite pattern of change in the electroretinogram. From the 7th to 9th days the electroretinogram consisted of slow, purely cornea-negative potentials. From the 9th to 10th days the responses were negative but included a prominent fast, negative component superimposed on the slow potentials. During the 11th to 17th days positive potentials appeared and developed. From the 20th day on, the typical electroretinogram of the adult obtained.