. The descent of man : and selection in relation to sex. Evolution; Natural selection; Heredity; Human beings. Chap. XIV. Ocelli. 429 matter being drawn towards a central point from a surrounding zone, which latter is thus rendered lighter; and, on the other hand, that a white spot is often formed by the colour being driven away from a central point, so that it accumulates in a surround- ing darker zone. In either case an ocellus is the result. The colouring matter seems to be a nearly constant quantity, but is redistributed, either centripetally or centrifugally. The feathers. Fig. Cyllo
. The descent of man : and selection in relation to sex. Evolution; Natural selection; Heredity; Human beings. Chap. XIV. Ocelli. 429 matter being drawn towards a central point from a surrounding zone, which latter is thus rendered lighter; and, on the other hand, that a white spot is often formed by the colour being driven away from a central point, so that it accumulates in a surround- ing darker zone. In either case an ocellus is the result. The colouring matter seems to be a nearly constant quantity, but is redistributed, either centripetally or centrifugally. The feathers. Fig. Cyllo leda, Linn., from a drawing by Mr. Triinen, shewing the extreme range of variation in the ocelli. A. Specimen, from Mauritius, upper surface of fore-wing. Ai. Specimen, from Natal, ditto. B. Specimen, from Java, upper surface of hind-wing. &. Specimen, from Mauritius, ditto. of the common guinea-fowl offer a good instance of white spots surrounded by darker zones; and wherever the Avhite spots are large and stand near each other, the surrounding dark zones become confluent. In the same wing-feather of the Argus pheasant dark spots may be seen surrounded by a pale zone, and white spots by a dark zone. Thus the formation of an ocellus in its most elementary state appears to be a simple affair. By what further steps the more complex ocelli, which are sur- rounded by many successive zones of colour, have been generated, I will not pretend to say. But the zoned feathers of the mongrels from differently coloured fowls, and the extraordinary variability of the ocelli on many Lepidoptera, lead us to conclude that their formation is not a complex process, but depends on some slight and graduated change in the nature of the adjoining Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Darwin, Charles, 1809-
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