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. 5-i. Cyllo leda, Linn., from a drawing by Mr. Trimen, shewing the extreme 



range of variation in the ocelli. 



A. Specimen, from Mauritius, upper B. Specimen, from Java, upper Mirface 



surface of fore-wing of hind-wing. 



AX Specimen, from Natal, ditto. Bl. Specimen, from Mauritius, ditto. 



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 

 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 api^ears 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 tissues. 



