4.28 The Descent of Man. Pakt 11 



iris, but the central spot is often surrounded by additional con- 

 centnc zones. The ocelli en the tail-coverts of the peacock offer 

 a familiar example, as well as those on the wings of the peacock- 

 butterfly (Vanessa). Mr. Trimen has given me a description of 

 a S. African moth (^Gyananin isis), allied to our Emperor moth, 

 in which a magnificeut ocellus occupies nearly the whole surface 

 of each hinder wing; it consists of a black centre, including a 

 semi-transparent crescentrshaped mark, surrounded by successive, 

 ochre-yellow, black, ochre-yellow, pink, white, pink, brown, and 

 whitish zones. Although we do not know the steps by which 

 these wonderfully beautiful and complex ornaments have been 

 developed, the process has probably been a simple one, at least 

 with insects ; for, as Mr. Trimen writes to me, " no characters of 

 " mere marking or coloration are so unstable in the Lepidoptera 

 " as the ocelli, both in number and size." Mr. Wallace, who 

 first called my attention to this subject, shewed me a series of 

 specimens of our common meadow-brown butterfly (/«ppaj-c/)«a 

 jixni.ra) exhibiting numerous gradations from a simple minute 

 black spot to an elegantly-shaded ocellus. In a S. African 

 butterfly {Cyllo leda, Linn.), belonging to the same family, the 

 ocelli are even still more variable. In some specimens (A, fig. 53) 

 large spaces on the upper surface of the wings are coloured 

 black, and include irregular white marks ; and from this state 

 a complete gradation can be traced into a tolerably perfect 

 ocellus (A'), and this results from the contraction of the irregular 

 blotches of colour. In another series of specimens a gradation 

 can be followed from excessively minute white dots, surrounded 

 by a scarcely visible black line (B), into perfectly symmetrical 

 and large ocelli (B'').^* In cases like these, the development 

 of a perfect ocellus does not i-equire a long course of \-ariation 

 and selection. 



"With birds and many other animals, it seems to follow from 

 the comparison of allied species that circular spots are often 

 generated by the breaking up and contraction of stripes. In the 

 Tragopan pheasant faint white lines in the female represent the 

 beautiful white spots in the male;^° and something of the same 

 kind may be observed in the two sexes of the Argus pheasant. 

 How€ver this may be, appearances strongly favour the belief that 

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



*^ This woodcut has been en- wing.s of this butterfly, in his 



graved from a beautiful drawing, ' Rhopalocera Africa; Australis," p. 



most kindiy made for me by Mr. 186. 



Trimen ; see also his description of *^ Jerdon, ' Birds of India,' vnl 



the wcaderful amc — it of variation iii. p. 617. 

 in tl»e eol.iration and shape of the 



