574 BIRD’S-EYE VIEWS. 
interlacing blood-vessels, and painted pitch-black all over. 
The deposit of pigmentary or black coloring matter is very 
heavy, and serves to absorb those rays of light not needed 
in vision. The choroid membrane lines all the inside of the 
eye as far forward as the edges of the bony plates, where it 
splits into two layers. The inner of these turns away from _ 
~ the wall of the ball, towards the axis or middle line of the 
eye, and in so doing becomes gathered in plice, or folds, 
much as the top of a bag is wrinkled by pulling the string. 
These radiating folds come from all around, to collect to- 
gether upon the rim of the crystalline lens (0), or rather of 
the delicate capsule (n)-that encloses the lens, and adhere 
there. Their terminations form what are called the ciliary 
processes (i, i). The outer layer also curls away from the 
sclerotic, and starts to go transversely across the eyeball, 
but ends at once in the iris. 
The iris (1,1) is the most exquisitely beautiful structure 
in a bird’s eye. It is the many-colored curtain that hangs 
vertically between the two apartments of the eye. It is the 
highly ornamented framework of the window of the ey® 
uniting the offices of sash and blind. The crystalline lens 18 
suspended in the round hole punched in the centre of the 
iris. Viewed in front, from the outside, the iris appears 3$ 
a colored circular band around the pupil. It seems to lie 
directly on the surface. But this is not so, for the cornea and 
its humors are between us and it. It is like the dial-plate 
of a watch, that we look straight at without noticing the 
crystal that is interposed. The central aperture through 
which come the shafts that the hands are fastened to, may ue 
likened to the pupil. Everybody knows what the “pupil 
is, in a vague way. It is the round black spot inside the 
colored rim of the iris; but few understand what the spot th 
The difficulty is, that the pupil is regarded as a materi! 
thing—a tissue, structure, or organ—when it is not. es 
the absence of matter. The round black spot called the 
pupil is not a “thing ;” it is a hole in a thing, —the hole 0 

