422 THE DESCENT OF MAN. 



ocelli on th<e feathers of various birds, on the hairy coats of some 

 mammals, on the scales of reptiles and fishes, on the skin of 

 amphibians, on the wings of many Lepidoptera and other Insects, 

 they deserve to be especially noticed. An ocellus consists of a 

 spot within a ring of another color, like the pupil within the 

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

 centric zones. The ocelli on 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 (Gyananis isis), allied to our Emperor moth, 

 in which a magnificent ocellus occupies nearly the whole surface 

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

 semi-transparent crescent-shaped 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, showed me a series of speci- 

 mens of our common meadow-brown butterfiy (Hipparchia janira) 

 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 colored 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 color. In another series of specimens a gradation can be fol- 

 lowed from excessively minute white dots, surrounded by a scarce- 

 ly visible black line (B), into perfectly symmetrical and large 

 ocelli (B-).'" In cases like these the development of a perfect 

 ocellus does not require a long course of variation 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. 



^ This woodcut has been engraved from a beautiful drawingr, most 

 kindly made for me by Mr. Trimen; see, also, his description of the 

 wonderful amount of variation in the coloration and shape of the 

 Xvingrs of this butterfly, in his 'Rhopalocera Africae Australis,' p. 1S6. 



" Jerdon, 'Birds of India,' vol. Hi. p. BIT. 



