EVE 229 
will doubtless find that artificial feathers can be made, even as 
artificial flowers now are, and there will be a fine opening for the 
ingenious inventor. The pity is that he does not at once begin. 
EYE. The eyeball of Birds is far less globular than that of 
Mammals, resembling rather the tube of a short and thick opera- 
glass. It consists externally of three successive portions. A basal 
or posterior, an intermediate, and an anterior portion. The wall of 
the anterior portion is formed by the transparent cornea, and is more 
strongly curved than that of the basal portion, which like the inter- 
mediate portion is formed by the white and opaque sclera. Within 
the walls of the sclera exists cartilage with occasional ossifications. 
Such an ossification, the posterior sclerotic ring, surrounds in many 
birds, especially in the Pici and in the Passeres, the entrance of -the 
optic nerve. Nearly all birds possess an anterior sclerotic ring which 
is composed of from 10 to 17, generally from 13 to 15, bony scales 
which overlap each other in various ways, and form the somewhat 
conical intermediate or connecting portion of the walls of the eye. 
The outer surface of the cornea is covered by the likewise quite 
transparent conjunctiva, a continuation of the mucous membrane 
lining the inside of the eyelids. The inner surface of the cornea 
is covered by the “membrana Descemeti,” a structureless film 
which seems to be the continuation of the chorioid membrane. 
The inner surface of the sclerotic wall is covered by the chorioid 
membrane, a thin membrane, which is rich in blood-vessels and is 
dark or black owing to the number of pigment-cells. It is morpho- 
logically the continuation of the pia mater or innermost sheath of 
the optic nerve, which enters the middle of the posterior segment 
of the eye and then spreads itself out as the retina upon the inner 
surface of the chorioid membrane. ‘The latter is consequently 
situated between the sclera and the retina. Level with the 
junction of the cornea and the sclera, i.e. at the anterior margin of 
the intermediate portion of the eye, the chorioid membrane leaves 
the wall of thé eye by turning away at a right angle and hanging 
like a circular curtain, the iris, over the anterior surface of the /ens, 
into the anterior chamber of the eye. The central hole in this 
diaphragma-like curtain is the pupil. The iris is a thin plate of 
connective tissue; its hinder surface is covered like the chorioid 
with a layer of black pigment, while its anterior side is coloured in 
various ways, either by pigment corpuscles or by coloured drops of 
fat. Often beautifully bright, it adds much to the expression of 
birds ; it is, for instance, vividly yellow in Lamprocolius, Botaurus, 
and Picus martius ; red in Chrysotis and in Nycticorax; green in 
the Cormorant ; white in the Grey Parrot and in Harelda; grey in 
Balearica pavonina and in Fratercula ; bluish in Cypselus ; black in 
Cacatua, and so on. In most young birds the colour of the iris is, 
‘iwisin Haveldg sad Febe Syaw-coloe in winter, dark hazel 
‘th summer. ERS. Elliot Bull- BO. Club, 20 Hay 1996. 
