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Summary.

  • 1
    The Lemuroidea examined are characterised by a retina of the nocturnal type.
  • 2
    flyctipithecus, n true Monkey, has a retina of the nocturnal type without macula or fovea.
  • 3
    The genern1is:ttion that a macula and fovea are found only in the retina when cones are present is confirmed.
  • 4
    An additional distinction between the diurnal and nocturnal retina is present in the size of the nuclear layers. The outer nuclear layer is the larger in the nocturnal: the inner is the larger in the diurnal. Put another way there are more percipient elements than conducting elements in the nocturnal; the reverse is the case in the diurnal retina.
  • 5
    An attempt has been made to arrange the Simiae examined in the order of retinal differentiation. Cemocebus ficliginosus possesses the purest cone retina and the most perfect foveal excavation. The differences are too slight and the layers too individually variable to attach much validity to the above tables.