OCELLI. 



423 



However this may be, appearances strongly favor the belief that 

 on the one hand, a dark spot is often formed by the coloring 

 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 color 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 



Fig. 



53. Cyllo leda, Linn., from a drawing by Mr. Trimen, showing 

 the extreme range of variation in the ocelli. 



A. Specimen, from Mauritius, up- 

 per surface of fore-wing. 

 A^ Specimen, from Natal, ditto. 



B. Specimen, from Java, upper 

 surface of hind- wing. 



B'. Specimen, from Mauritius, 

 ditto. 



coloring matter seems to be a nearly constant quantity, but is 

 redistributed, either centripetally or centrifugally. The feathers 

 of the common guinea-fowl offer a good instance of white spots 

 surrounded by darker zones; and wherever the white spots are 

 large and stand near each other, the surrounding dark zones 

 become confluent. In the same wing-feather of the Argus pheas- 

 ant 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 surrounded by 

 many successive zones of color, have been generated, I will not 

 pretend to say. But the zoned feathers of the mongrels from dif- 

 ferently colored fowls, and the extraordinary variability of the 



