smaller spots, so that two or three rows run down to the same ocellus.
There still remains another very curious point, first observed by Mr.
T.W. Wood (51. The Field, May 28, 1870.), which deserves attention.
In a photograph, given me by Mr. Ward, of a specimen mounted as in the
act of display, it may be seen that on the feathers which are held
perpendicularly, the white marks on the ocelli, representing light
reflected from a convex surface, are at the upper or further end, that
is, are directed upwards; and the bird whilst displaying himself on the
ground would naturally be illuminated from above. But here comes the
curious point; the outer feathers are held almost horizontally, and
their ocelli ought likewise to appear as if illuminated from above, and
consequently the white marks ought to be placed on the upper sides of
the ocelli; and, wonderful as is the fact, they are thus placed! Hence
the ocelli on the several feathers, though occupying very different
positions with respect to the light, all appear as if illuminated from
above, just as an artist would have shaded them. Nevertheless they are
not illuminated from strictly the same point as they ought to be; for
the white marks on the ocelli of the feathers which are held almost
horizontally, are placed rather too much towards the further end; that
is, they are not sufficiently lateral. We have, however, no right to
expect absolute perfection in a part rendered ornamental through sexual
selection, any more than we have in a part modified through natural
selection for real use; for instance, in that wondrous organ the human
eye. And we know what Helmholtz, the highest authority in Europe on the
subject, has said about the human eye; that if an optician had sold him
an instrument so carelessly made, he would have thought himself fully
justified in returning it. (52. Popular Lectures on Scientific
Subjects, Eng. trans. 1873, pp. 219, 227, 269, 390.)
We have now seen that a perfect series can be followed, from simple
spots to the wonderful ball-and-socket ornaments. Mr. Gould, who kindly
gave me some of these feathers, fully agrees with me in the
completeness of the gradation. It is obvious that the stages in
development exhibited by the feathers on the same bird do not at all
necessarily shew us the steps passed through by the extinct progenitors
of the species; but they probably give us the clue to the actual steps,
and they at least prove to demonstration that a gradation is possible.
Bearing in mind how carefully the male Argus pheasant displays his
plumes before the female, as well as the many facts rendering it
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