When Frightened, It Attempts
To Avoid Discovery By Feigning Death, With Outstretched
Legs, Depressed Body, And Closed Eyes:
If further
molested, it buries itself with great quickness in the loose
sand.
This lizard, from its flattened body and short legs,
cannot run quickly.
I will here add a few remarks on the hybernation of animals
in this part of South America. When we first arrived
at Bahia Blanca, September 7th, 1832, we thought nature
had granted scarcely a living creature to this sandy and dry
country. By digging, however, in the ground, several insects,
large spiders, and lizards were found in a half-torpid
state. On the 15th, a few animals began to appear, and by
the 18th (three days from the equinox), everything announced
the commencement of spring. The plains were ornamented
by the flowers of a pink wood-sorrel, wild peas,
cenotherae, and geraniums; and the birds began to lay their
eggs. Numerous Lamellicorn and Heteromerous insects, the
latter remarkable for their deeply sculptured bodies, were
slowly crawling about; while the lizard tribe, the constant
inhabitants of a sandy soil, darted about in every direction.
During the first eleven days, whilst nature was dormant, the
mean temperature taken from observations made every two
hours on board the Beagle, was 51 degs.; and in the middle of
the day the thermometer seldom ranged above 55 degs. On the
eleven succeeding days, in which all living things became so
animated, the mean was 58 degs., and the range in the middle
of the day 7 between 60 and 70 degs. Here, then, an
increase of seven degrees in mean temperature, but a greater one
of extreme heat, was sufficient to awake the functions of life.
At Monte Video, from which we had just before sailed, in
the twenty-three days included between the 26th of July
and the 19th of August, the mean temperature from 276
observations was 58.4 degs.; the mean hottest day being
65.5 degs., and the coldest 46 degs. The lowest point to
which the thermometer fell was 41.5 degs., and occasionally
in the middle of the day it rose to 69 or 70 degs.
Yet with this high temperature, almost every beetle, several
genera of spiders, snails, and land-shells, toads and
lizards were all lying torpid beneath stones. But
we have seen that at Bahia Blanca, which is four degrees
southward and therefore with a climate only a very little
colder, this same temperature with a rather less extreme
heat, was sufficient to awake all orders of animated beings.
This shows how nicely the stimulus required to arouse hybernating
animals is governed by the usual climate of the
district, and not by the absolute heat. It is well known that
within the tropics, the hybernation, or more properly aestivation,
of animals is determined not by the temperature, but
by the times of drought. Near Rio de Janeiro, I was at first
surprised to observe, that, a few days after some little
depressions had been filled with water, they were peopled by
numerous full-grown shells and beetles, which must have
been lying dormant. Humboldt has related the strange accident
of a hovel having been erected over a spot where a
young crocodile lay buried in the hardened mud. He adds,
"The Indians often find enormous boas, which they call Uji
or water serpents, in the same lethargic state. To reanimate
them, they must be irritated or wetted with water."
I will only mention one other animal, a zoophyte (I believe
Virgularia Patagonica), a kind of sea-pen. It consists
of a thin, straight, fleshy stem, with alternate rows of polypi
on each side, and surrounding an elastic stony axis, varying
in length from eight inches to two feet. The stem at one
extremity is truncate, but at the other is terminated by a
vermiform fleshy appendage. The stony axis which gives
strength to the stem may be traced at this extremity into a
mere vessel filled with granular matter. At low water hundreds
of these zoophytes might be seen, projecting like stubble,
with the truncate end upwards, a few inches above the
surface of the muddy sand. When touched or pulled they
suddenly drew themselves in with force, so as nearly or quite
to disappear. By this action, the highly elastic axis must
be bent at the lower extremity, where it is naturally slightly
curved; and I imagine it is by this elasticity alone that the
zoophyte is enabled to rise again through the mud. Each
polypus, though closely united to its brethren, has a distinct
mouth, body, and tentacula. Of these polypi, in a large
specimen, there must be many thousands; yet we see that
they act by one movement: they have also one central axis
connected with a system of obscure circulation, and the ova
are produced in an organ distinct from the separate
individuals. [19] Well may one be allowed to ask, what is an
individual? It is always interesting to discover the foundation
of the strange tales of the old voyagers; and I have no doubt
but that the habits of this Virgularia explain one such case.
Captain Lancaster, in his voyage [20] in 1601, narrates that on
the sea-sands of the Island of Sombrero, in the East Indies,
he "found a small twig growing up like a young tree, and
on offering to pluck it up it shrinks down to the ground,
and sinks, unless held very hard. On being plucked up, a
great worm is found to be its root, and as the tree groweth
in greatness, so doth the worm diminish, and as soon as the
worm is entirely turned into a tree it rooteth in the earth,
and so becomes great. This transformation is one of the
strangest wonders that I saw in all my travels: for if this
tree is plucked up, while young, and the leaves and bark
stripped off, it becomes a hard stone when dry, much like
white coral:
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