230 EVE 
however, brown, and attains brighter tints with maturity occasionally 
in the male only ; for instance, yellow in the males of Ploceus, but 
brown in the females ; 
greyish-brown in the 
females and young of 
the Golden Oriole, and 
carmine-red in the old 
males. 
The iris contains a 
sphincter and a dilator 
muscle. The sphincter 
consists of concentrical 
fibres which constitute 
a considerable portion 
of the whole iris, while 
the fibres of the dilator 
are arranged in a radi- 
ating way. Those of 
Prey. About twice the natural size. (After H. Muller.) the former are supplied 
A.ch. Anterior chamber; P.ch. Posterior chamber; C, by branches from the 
Cornea; Ch. Chorioid; Co, Conjunctiva; ¢e.m. Crampton’s oculomotory or third 
muscle; 7, Iris; L, Lens; P, Pecten; N.O. Optic nerve ; 
R, Retina; Se. Sclerotic, with embedded osseous ring. 
HorIZONTAL SECTION THROUGH THE EYE OF A BIRD-OF- 
pair of cranial nerves, 
; and are in Birds, in 
opposition to the Mammalia, under the control of the will. The 
dilator muscle is supplied by sympathetic nerve fibres. Both 
sorts of nerve fibres enter the posterior wall of the eye, ascend 
between the chorioid and sclera, and supply these parts together 
with the iris and the ciliary muscle. The shape of the pupil, 
when fully dilated, is round in all birds; when partly contracted 
it is either likewise round in most birds, or obliquely oval as in 
some Gallinzi. 
The corpus ciliare is that part of the chorioid which covers the 
1 Numerous notes concerning the colour of the iris in reference to age and sex 
have been published by Th. A. Bruhin in Zoolog. Garten, 1870, pp. 290-295. A 
curious observation by the late Mr. J. H. Gurney is recorded in Mr. Southwell’s 
continuation of Stevenson’s Birds of Norfolk (iii. p. 207). On removing a living 
male Pochard (Fuligula ferina) from one pond to another, while the bird was held 
in the hand the ordinary cherry-colour of its irides was seen to be replaced by 
yellow, hardly, if at all, tinged with red. When this bird was released, the 
normal colour was gradually but speedily resumed. In this species it will be 
remembered the red iris is peculiar to the male, that of the female being of a dark 
brown. 
The four nearly-allied species of the genus Hypsipetes inhabiting Madagascar 
and the Mascarene Islands differ, according to the observation of Sir Edward 
Newton (Orn. Miscell. ii. p. 52, pl. xlii.), in the colour of their irides, which in H. 
madagascariensis are bright red, in H. borbonicus whitish, in H. olivaceus (of 
Mauritius) orange, and in H. crassirostris (from the Seychelles) dark red. 
