My head keeps very rocky
and wretched, but I am better,--Ever yours most truly,
C. DARWIN.
* * * * *
_Holly House, Barking, E. March 3, 1872._
Dear Darwin,--Many thanks for your new edition of the "Origin," which I
have been too busy to acknowledge before. I think your answer to Mivart
on the initial stages of modification ample and complete, and the
comparison of whale and duck most beautiful. I always saw the fallacy of
these objections, of course. The eye and ear objection you have not so
satisfactorily answered, and to me the difficulty exists of how _three
times over_ an organ of sight was developed with the apparatus even
approximately identical. Why should not, in one case out of the three,
the heat rays or the chemical rays have been utilised for the same
purpose, in which case no translucent media would have been required,
and yet vision might have been just as perfect? The fact that the eyes
of insects and molluscs are transparent to us shows that the very same
limited portion of the rays of the spectrum is utilised for vision by
them as by us.
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