| OCR Text |
Show 132 SEXUAL SELECTION: BIRDS. PART H. 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 small part black which is white in the parent-species.44 Formation and variability of the Ocelli or eye-like Spols on lhe 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 colour, like the pupil within the iris, but the central spot is often surrounded 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-butterfl.y (Vanessa). Mr. Trimen has given me a description of aS. 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 centre, 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 at least with insects has probably been a simple one; 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 "numbel· and size." Mr. vVallace, who first called my attention to this subject, shewed me a series of specimens of our common meadow-brown butterfly (Hip- H Bcchstein, 'Naturgcschichto Dcutschlo.nds,' B. iv. 1705, s. 3J, on o. sub-variety of the Monck pigeon. CHAr. xrv. OCELLI. 133 parchia J anira) exhibiting numerous gradations from a simple minute black spot to an elegantly-shaded ocellus: In a S. African b.utterfly (Cyllo Leda, Linn.) belongmg to the same family, the ocelli are even still more variable. In some specimens (A, fig. 52) large spaces on the upper surface of the wings are coloured bl~ck, and include irregular white marks ; and from this state a complete gradation can be traced into a A J3l n Fig. 52. Cyllo lcda, Linn., from a drawing by Mr. Trimen, shewing the extreme range of variation in the ocelli . .A. Specimen, from Mauritius upper 13. Spccill?en, from Java, upper surface surface of fore·wing. ' of Jund·wing . .A.l, Specimen, from Natal, ditto. lll. Specimen, fi·om Mauritius, ditto. tolerably perfect (A'L) ocellus, and this results from the contraction of the irregular blotches of colour. In another series of specimens a gradation can be followed from exce~s~vely minute white dots, surrounded by a sc~rcely VIsible black line (B), into perfectly symmetncal and large ocelli (B 1 ). 45 In cases like these, the • 15 'fhis woodcut has been engraved from a bco.utiful drawing most kmdly made for me by Mr. Trimen ; see also his description ~f the |
