certain
times of the year vanishes suddenly through chasms under water, sucking
the fish down with it; and after a certain time boils suddenly up again
from the depths, bringing back with it the fish, who have been swimming
comfortably all the time in a subterranean lake; and bringing back, too
(and, extraordinary as this story is, there is good reason to believe it
true), live wild ducks who went down small and unfledged, and come back
full-grown and fat, with water-weeds and small fish in their stomachs,
showing they have had plenty to feed on underground. But--and this is
the strangest part of the story, if true--they come up unfledged just as
they went down, and are moreover blind from having been so long in
darkness. After a while, however, folks say their eyes get right, their
feathers grow, and they fly away like other birds.

Neither would you be surprised (if you recollect that Madam How is a very
old lady indeed, and that some of her work is very old likewise) at that
Mammoth Cave in Kentucky, the largest cave in the known world, through
which you may walk nearly ten miles on end, and in which a hundred miles
of gallery have been explored already, and yet no end found to the cave.
In it (the guides will tell you) there are "226 avenues, 47 domes, 8
cataracts, 23 pits, and several rivers;" and if that fact is not very
interesting to you (as it certainly is not to me) I will tell you
something which ought to interest you: that this cave is so immensely old
that various kinds of little animals, who have settled themselves in the
outer parts of it, have had time to change their shape, and to become
quite blind; so that blind fathers and mothers have blind children,
generation after generation.

There are blind rats there, with large shining eyes which cannot
see--blind landcrabs, who have the foot-stalks of their eyes (you may see
them in any crab) still left; but the eyes which should be on the top of
them are gone. There are blind fish, too, in the cave, and blind
insects; for, if they have no use for their eyes in the dark, why should
Madam How take the trouble to finish them off?

One more cave I must tell you of, to show you how old some caves must be,
and then I must stop; and that is the cave of Caripe, in Venezuela, which
is the most northerly part of South America. There, in the face of a
limestone cliff, crested with enormous flowering trees, and festooned
with those lovely creepers of which you h