The Descent of Man

shades off downwards into a pale-leaden hue,
and this into yellowish and brown tints, which
insensibly become darker and darker towards
the lower part of the ball. It is this shading
which gives so admirably the effect of light
shining on a convex surface. If one of the balls
be examined, it will be seen that the lower part
is of a brown tint and is indistinctly separated
by a curved oblique line from the upper part,
which is yellower and more leaden; this curved
oblique line runs at right angles to the longer
axis of the white patch of light, and indeed of
all the shading; but this difference in colour,
which cannot of course be shewn in the woodcut,
does not in the least interfere with the perfect
shading of the ball. It should be particularly
observed that each ocellus stands in obvious
connection either with a dark stripe, or with a
longitudinal row of dark spots, for both occur
indifferently on the same feather. Thus in Fig.
57 stripe A runs to ocellus a; B runs to ocellus b;
stripe C is broken in the upper part, and runs