CHAPTER XII. 



LINEAR SERIES continued. COLOUR-MARKINGS. 



OCELLAi; M AllKIXGS 1 , ESPECIALLY THOSE OF LEPIDOPTERA. 



UP<'\ the bodies of animals belonging to many classes are 

 markings which consist of a central patch of colour surrounded by 

 a variable number uf concentric rings of different colours. Such 

 markings arc known as ocelli or eye-spots from their resemblance 

 to the pupil and iris of vertebrates. Eye-spots are perhaps best 

 known in Lepidoptera, but similar markings are not unfrequent in 

 other groups and especially on the feathers of Birds and in Fishes. 



In one of the best known chapters in the Descent of Man' the 

 nature and mode of evolution of these markings is the subject of 

 a full discus-ion, the case of eye-spots on feathers being chiefly 

 r.-ikeii in illustration. As is well known, Darwin by the compara- 

 tive method, comparing the eye-spots found in different species, on 

 the different feathers of the same bird, or on different parts of the 

 same feather, tiiiind that it was possible to construct a complete 

 progression from a plain spot to a fully-formed ocellus. Though 

 no one examining such a series can possibly doubt that the simple 

 -pot and the fully-formed ocellus are really of the same nature and 

 that the one represents a modification of the other, there remains 

 nevertheless the difficulty that members of a series of parts cannot 

 be assumed to represent conditions through which the other mem- 

 1" rs of the same series have passed, and it is of course clear that 

 the conditions found in some forms do not necessarily correspond 

 with pliylogeiietic. phases of other forms. In the present instance 

 however Darwin is not specially urging this view, but brings 

 for wan I the comparative evidence chiefly in illustration of the 

 possibility that such structures may exist in an imperfect state 

 and so may be conceived of as having had a gradual origin. 



1 The evidence concerning eyespots of Lepidoptera is taken here because eyespots 

 when rrpi'iitr.l in MTH s, though borne on appendicular parts, are nevertheless 

 arranged chirlly with roft-n-nce to the chief axis of symmetry of the body. In some 

 ft\v forms, !. ;i. 'I'lii/iii-tif, there is a conspicuous Minor Symmetry within the limits 

 uf ;i .-ingle wing (tin- posterior), but this is not often the case. 



- Dc.-r.-nt i Man, 1871, n. pp. 132153. 



