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The presence of cones in potto's retina has been proved beyond doubt although they are very restricted in number (1 cone for 300 rods). Morphologically speaking there is no point in calling these cones “rudimentary” except for their slender outer segment. There are red sensitive elements in that retina at wavelengths beyond the spectral sensitivity of visual purple and it is tempting to assume that these elements are cones. The ERG evoked from these elements by red light differs from that in response to white and blue light. They dark-adapt faster than the receptors sensitive to blue and white flashes. However in some of their properties, for example fusion frequency, these cones behave like rods in other species. As these few cones seem to activate the bipolar cells nearly as effectively as the numerous rods, it is suggested that these cones may be responsible for day vision in the potto.

The succession of amplitudes constituting spontaneous electroencephalographic activity cannot be regarded as a strictly normal distribution. Spontaneous activity and the evoked response are not independent. The signal (evoked response)is, in some cases, non-stationary. The average visual-evoked response comprises several successive temporal fragments of which the stationary character varies. This variability of the average visual-evoked response argues in favour of the complexity of its genesis.

Various statistical discrimination indices reveal deflections regarded as significant before the 20th ms after stimulation (probably equivalent to Bickford responses or subcortical activity) and between the 20th and 23rd ms (early fractions of MVER). The independence of signal and noise is discussed. Considerations concerning the calculation of retinocortical time are developed.

The authors confirm the presence of very early deflection (before the 20th msec. after the flash). They probably have their origin under the cortex. The curves showing the attenuation of the spontaneous activity during the summation and those illustrating the evolution of the variancy of the early portions of the VER are comparable. By contrast, the stability of the curves related to later fractions state problems about the often pretented independancy of spontaneous and evoked activities.