132 
SEXUAL SELECTION : BIRDS. 
Part B. 
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.^^ 
Formation and variahiliiy of the Ocelli or eye-like 
Spots on the Flumage 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 con- 
sists of a spot within a ring of another colour, like the 
pupil within the iris, but the central spot is often sur- 
rounded 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 S. 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 
number and size.” Mr. Wallace, who first called my 
attention to this subject, shewed me a series of spech 
mens of our common meadow-brown butterfly (Hip- 
Bechstein, ‘ Naturgeschichte Deutschlands,’ B. iv. 1795, s. 31, on 
a sub-variety of the Monck pigeon. 
