Note AB — Chapter V · EXPLANATION OF THE OBSERVATIONS

Königshöfer, who as we have already said, seconds the explanation given by the ophthalmologist Berlin (and who confounds "Butzenscheiben" astigmatism with the common, so-called regular form), believes[54] that not only astigmatism but also the shape of the blind-spot of the eye must be taken into consideration. This portion of the retina, where the fibres of the optic nerve enter the eye (and called "blind-spot" because there are no cells there that are sensitive to light) is very nearly circular in man, but differs in shape in the different species of animals. Königshöfer thought he had discovered that a relatively elongated blind spot was favorable to keenness of vision. If we place the mammalia in series on the basis of their relative keenness of vision, he says, we would find that this series is identical with the one in which they are grouped with reference to the form of the blind-spot from the circular up to the most elongated. (In such a series the marmot takes the place of honor.)

This exposition is not very