The typical vertebrate electroretinogram obtained upon illumination of the eye is a complex polyphasic wave. After a short latent period there appears a small deflection (a-wave)2 indicating a condition of negativity of the posterior portion of the eyeball. This is then followed by a rapid positive deflection (b-wave) and a slow secondary positive rise (c-wave). When stimulation ceases there occurs, after a short latent period, another positive rise (d-wave) whose magnitude and rate of rise depend on a number of factors including the type of eye, the duration and intensity of the stimulating light, and the degree of light or dark adaptation of the eye. The literature on this subject includes studies on a number of vertebrates and has been adequately summarized by Day ( '15) ; Chaffee, Bovie and Hampson ( '23) ; Kohlrausch ( '31) and Granit ('36).
The electrical potentials associated with the invertebrate eye have not been so extensively studied. However, a number of early workers including Beck (1899) ; v. Briicke and Garten ( '07) ; Piper ( '11) and Frohlich ( '13) noted certain similarities in the electric responses from the eyes of certain invertebrates and those obtained from vertebrates. More recently Hartline ( '28) found the electrical changes in the compound eye of a 'Aided by a grant from the Rockefeller Foundation for research in cellular. a The designations employed by Granit ( '32) are given here. physiology. 39 ' The data for this summary have been obtained from the papers of Gotch ( '03)' Einthoveii and Jolly ( '08)' Hartline ( '25)' Kohlrausch ( '31)' Granit ('32, '35).