摘要：

SYNOPSISAfter formaldehyde fixation, three types of cone can be described in the retina of man and monkey. The differences are due to a fixation artifact but represent an inherent non-identity, which is imperceptible after better fixation. There is no evidence to suggest that those three types perform different functions in colour vision and it is more likely that they represent different stages of activity or degeneration.The outer segment of the cones is composed of a uniform core surrounded by a cell membrane, which is discontinuously thickened to form a thread disposed as a series of rings or a spiral, which is myelin in nature and has a high refractive index. Some of the rods show a similar structure of the outer segment, particularly in man and the baboon. Although unpigmented, the thread appears opaque when sections are examined in a mountant of low refractive index.

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