132 
SEXUAL SELECTION : BIRDS. 
fit 1 
outer webs of the two outer tail-feathers white . ^ 
there is a sub-variety having a white instead of ^ 
tail, with precisely that small part black which i s ' 
in the parent-species . 44 
Formation and variability of the Ocelli or e H ^ ^ 
Spots on the Plumage of Birds. — As no ornamec^. .,. 
more beautiful than the ocelli ontlie feathers of ' ‘‘ g. 
- on 1 
■■br 
birds, on the hairy coats of some mammals, 
scales of reptiles and fishes, on the skin of amph 1 
on the wings of many Lepidoptera and other i j- 
they deserve to be especially noticed. An ocelhi 8 ^],,' 
sists of a spot within a ring of another colour 
like 
pupil within the iris, but the central spot is 
JbM 
rounded by additional concentric zones. The ° cC ^,lo 
the tail-coverts of the peacock offer a familiar eX!l ' 
as well as those on the wings of the peacock-b ut ^ 
(Vanessa). Mr. Trimen has given me a descrip 11 / 
a S. African moth ( Gynanisa Isi.s), allied to our EUT 
moth, in which a magnificent ocellus occupies ue !)1 ^ 
whole surface of each hinder wing ; it consists of 
centre, including a semi-transparent crescent-* 
mark, surrounded by successive ochre-yellow, y. 
ochre-yellow, pink, white, pink, brown, and whitish * ^ 
Although we do not know the steps by which ^ 
wonderfully-beautiful and complex ornaments ha'^l; 
developed, the process at least with insects has p J ° ]J)t ' 
been a simple one ; for, as Mr. Trimen writes 
s to 
“ no characters of mere marking or coloration ^ 
“ unstable in tlie Lepidoptera as the ocelli? h° ^ 
“ number and size.” Mr. Wallace, ’ " ' "" 1 L 
who first calk .j- 
attention to this subject, shewed me a series 
of * 
mens of our common meadow-brown butterfly 
44 Bechstein. ‘ Nnturgpsehichte Deutsclilands,’ B. iv. 1”3 J 
a suk-vuriety of the Monck pigeon. 
(W 
„ 8 t' 
