tioned to
him an analogy which has struck me much, now that we know that sheep-pox
is fungoid; and this analogy pleased him. It is that of fairy rings,
which are believed to spread from a centre, and when they intersect the
intersecting portion dies out, as the mycelium cannot grow where it has
grown during previous years. So, again, I have never seen a ring within
a ring; this seems to me a parallel case to a man commonly having the
smallpox only once. I imagine that in both cases the mycelium must
consume all the matter on which it can subsist.

LETTER 779. TO A. GAPITCHE.

(779/1. The following letter was written to the author (under the
pseudonym of Gapitche) of a pamphlet entitled "Quelques mots sur
l'Eternite du Corps Humaine" (Nice, 1880). Mr. Gapitche's idea was
that man might, by perfect adaptation to his surroundings, indefinitely
prolong the duration of life. We owe Mr. Darwin's letter to the kindness
of Herr Vetter, editor of the well-known journal "Kosmos.")

Down, February 24th, 1880.

I suppose that no one can prove that death is inevitable, but the
evidence in favour of this belief is overwhelmingly strong from the
evidence of all other living creatures. I do not believe that it is by
any means invariably true that the higher organisms always live longer
than the lower ones. Elephants, parrots, ravens, tortoises, and some
fish live longer than man. As evolution depends on a long succession of
generations, which implies death, it seems to me in the highest degree
improbable that man should cease to follow the general law of evolution,
and this would follow if he were to be immortal.

This is all that I can say.

LETTER 780. TO J. POPPER.

(780/1. Mr. Popper had written about a proposed flying machine in which
birds were to take a part.)

Down, February 15th, 1881.

I am sorry to say that I cannot give you the least aid, as I have never
attended to any mechanical subjects. I should doubt whether it would be
possible to train birds to fly in a certain direction in a body, though
I am aware that they have been taught some tricks. Their mental powers
are probably much below those of mammals. It is said, and I suppose
truly, that an eagle will carry a lamb. This shows that a bird may have
great power for a short distance. I cannot remember your essay with
sufficient distinctness to make any remarks on it. When a man is old and
works hard, one subject drives another out of his head.

LETTER 7