48G THE DESCENT OF MAN. 



fereut tint. Here is a more curious case, in which certain 

 marks are retained, though colored in a manner almost 

 exactly the opposite of what is natural ; the aboriginal 

 pigeon has a blue tail, with the terminal halves of the outer 

 webs of the two outer tail-feathers white ; now there 

 is a sub - variety having a white instead of a blue tail, 

 with precisely that part black which is white in the parent- 

 species." * 



Formation and Variability of the Ocelli or Eye- Like 

 Spots on the Plumage of Birds. As no ornaments are 

 more beautiful than the ocelli on the 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 surrouded by additional concentric 

 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 South African moth (Gynanisa 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 ocher- 

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

 whitish zones. Although we do not know the steps by 

 which these wonderfully beautiful and complex orna- 

 ments 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 specimens of our 

 common meadow-brown butterfly (Hipparcliia janira) 

 exhibiting numerous gradations from a simple minute black 

 spot to an elegantly shaded ocellus. In a South African 

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

 the ocelli are even still more variable. In some specimens 





*Bechstein, " Naturgeschichte Deutschlands," B. iv, 1795, s. 81, 

 on a sub-variety of the Monck pigeon. 





